INCOMPLETE SESSION. hit wall-clock budget (SIGTERM). The transcript below is usable but may be missing the agent's final tool calls or summary. Don't score this run as a clean failure or success.
solution.py
final answer
benchmark.log
check.log
result.json
"""Paged-attention decode kernel for SM120 (RTX PRO 6000 Blackwell).
Flash-decoding style split-K CUDA kernel (torch.utils.cpp_extension.load_inline):
- One threadblock per (batch, kv_head, split). Each block streams its chunk of
the KV cache exactly once (K and V share a 512B segment, gathered via the
page table staged in shared memory), computes online softmax for the
G = num_heads/num_kv_heads grouped query heads with 8/16B vector loads and
a 2-stage register prefetch pipeline.
- Split partials (fp32 O, m, l) are merged by the LAST finishing block of each
(batch, kv_head) group — detected with an auto-resetting atomicInc semaphore
— so the whole decode is a single kernel launch.
"""
import math
import os
import torch
import torch.nn as nn
OP_TYPE = "attention"
SUPPORTED_PRECISIONS = ["bf16"]
HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]
# --- Shape knobs (kept for interface parity with reference.py) -------------
BATCH = 8
NUM_HEADS = 32
NUM_KV_HEADS = 8
HEAD_DIM = 128
SEQ_LEN = 1024
PAGE_SIZE = 16
_CPP_SRC = r"""
#include <torch/extension.h>
void paged_decode(at::Tensor q, at::Tensor kv, at::Tensor bt, at::Tensor sl,
at::Tensor out, at::Tensor o_part, at::Tensor ml, at::Tensor sem,
int64_t S, int64_t chunk, int64_t nwarps, int64_t pf, double qscale);
"""
_CUDA_SRC = r"""
#include <torch/extension.h>
#include <ATen/cuda/CUDAContext.h>
#include <cuda_bf16.h>
using bf16 = __nv_bfloat16;
using bf162 = __nv_bfloat162;
#define DEVINL __device__ __forceinline__
template <int BYTES> struct VecT;
template <> struct VecT<8> { using type = uint2; };
template <> struct VecT<16> { using type = uint4; };
template <int E>
DEVINL void unpack_bf16(const void* src, float* dst) {
#pragma unroll
for (int i = 0; i < E / 2; ++i) {
float2 t = __bfloat1622float2(reinterpret_cast<const bf162*>(src)[i]);
dst[2 * i] = t.x;
dst[2 * i + 1] = t.y;
}
}
// Maximum pages a single chunk may span (chunk <= 4096 tokens, page 16).
#define MAX_CHUNK_PAGES 256
#define NEG_INF (-1e30f)
template <int D, int G, int NWARPS, int PF>
__global__ void __launch_bounds__(NWARPS * 32)
decode_split_kernel(const bf16* __restrict__ q,
const bf16* __restrict__ kvc,
const int* __restrict__ block_table,
const int* __restrict__ seq_lens,
bf16* __restrict__ o_part, // (B, Hkv, S, G, D) normalized
float* __restrict__ ml_part, // (B, Hkv, S, G, 2)
unsigned* __restrict__ sem, // (B, Hkv)
bf16* __restrict__ out, // (B, H, D)
const int Hkv, const int S, const int chunk,
const int max_blocks, const float qscale) {
constexpr int TG = (G * D) / 32; // lanes cooperating on one token
constexpr int E = D / TG; // elems per lane per K (or V) vector
constexpr int TPW = 32 / TG; // tokens per warp per iteration
constexpr int NS = NWARPS * TPW; // token streams per block
using KVec = typename VecT<E * 2>::type;
static_assert(E == 4 || E == 8, "bad config");
const int split = blockIdx.x;
const int kvh = blockIdx.y;
const int b = blockIdx.z;
const int H = Hkv * G;
const int len = seq_lens[b];
const int Sb = min(S, (len + chunk - 1) / chunk);
const int t0 = split * chunk;
if (t0 >= len) return;
const int tend = min(t0 + chunk, len);
__shared__ int sm_pages[MAX_CHUNK_PAGES];
__shared__ float sm_m[NWARPS][G];
__shared__ float sm_l[NWARPS][G];
__shared__ float sm_o[NWARPS][G][D];
__shared__ unsigned sm_last;
const int warp = threadIdx.x >> 5;
const int lane = threadIdx.x & 31;
const int grp = lane / TG;
const int gl = lane - grp * TG;
const int stream = warp * TPW + grp;
{
const int p0 = t0 >> 4;
const int np = ((tend + 15) >> 4) - p0;
const int* bt = block_table + (int64_t)b * max_blocks + p0;
for (int i = threadIdx.x; i < np; i += NWARPS * 32) sm_pages[i] = bt[i];
}
__syncthreads();
// Query fragment for this lane (scaled by softmax scale * log2(e)).
float qr[G][E];
{
const bf16* qb = q + ((int64_t)b * H + (int64_t)kvh * G) * D + gl * E;
#pragma unroll
for (int g = 0; g < G; ++g) {
KVec v = *reinterpret_cast<const KVec*>(qb + g * D);
float tmp[E];
unpack_bf16<E>(&v, tmp);
#pragma unroll
for (int e = 0; e < E; ++e) qr[g][e] = tmp[e] * qscale;
}
}
float m[G], l[G], o[G][E];
#pragma unroll
for (int g = 0; g < G; ++g) {
m[g] = NEG_INF;
l[g] = 0.f;
#pragma unroll
for (int e = 0; e < E; ++e) o[g][e] = 0.f;
}
const int64_t slot_stride = (int64_t)Hkv * (2 * D);
const int64_t kvh_off = (int64_t)kvh * (2 * D) + gl * E;
const unsigned grp_mask =
(TG == 32) ? 0xffffffffu : (((1u << TG) - 1u) << (grp * TG));
// PF-stage software pipeline: K/V for token t prefetched PF*NS ahead.
auto addr = [&](int tok) {
return kvc + (int64_t)sm_pages[(tok - t0) >> 4] * (16 * slot_stride) +
(tok & 15) * slot_stride + kvh_off;
};
KVec kb[PF], vb[PF];
{
int tp = t0 + stream;
#pragma unroll
for (int p = 0; p < PF; ++p, tp += NS) {
if (tp < tend) {
const bf16* kp = addr(tp);
kb[p] = __ldcs(reinterpret_cast<const KVec*>(kp));
vb[p] = __ldcs(reinterpret_cast<const KVec*>(kp + D));
}
}
}
int t = t0 + stream;
while (t < tend) {
#pragma unroll
for (int p = 0; p < PF; ++p, t += NS) {
if (t >= tend) break;
const KVec ck = kb[p], cv = vb[p];
const int tn = t + PF * NS;
if (tn < tend) {
const bf16* kp = addr(tn);
kb[p] = __ldcs(reinterpret_cast<const KVec*>(kp));
vb[p] = __ldcs(reinterpret_cast<const KVec*>(kp + D));
}
float kf[E], vf[E];
unpack_bf16<E>(&ck, kf);
unpack_bf16<E>(&cv, vf);
float s[G];
#pragma unroll
for (int g = 0; g < G; ++g) {
float acc = 0.f;
#pragma unroll
for (int e = 0; e < E; ++e) acc = fmaf(qr[g][e], kf[e], acc);
s[g] = acc;
}
#pragma unroll
for (int off = TG / 2; off > 0; off >>= 1) {
#pragma unroll
for (int g = 0; g < G; ++g)
s[g] += __shfl_xor_sync(grp_mask, s[g], off);
}
#pragma unroll
for (int g = 0; g < G; ++g) {
const float mn = fmaxf(m[g], s[g]);
const float sc = exp2f(m[g] - mn);
const float pr = exp2f(s[g] - mn);
l[g] = fmaf(l[g], sc, pr);
m[g] = mn;
#pragma unroll
for (int e = 0; e < E; ++e) o[g][e] = fmaf(o[g][e], sc, pr * vf[e]);
}
}
}
// Merge the TPW token streams within each warp (all lanes redundantly).
#pragma unroll
for (int off = TG; off < 32; off <<= 1) {
#pragma unroll
for (int g = 0; g < G; ++g) {
const float mo = __shfl_xor_sync(0xffffffffu, m[g], off);
const float lo = __shfl_xor_sync(0xffffffffu, l[g], off);
const float M = fmaxf(m[g], mo);
const float wa = exp2f(m[g] - M);
const float wb = exp2f(mo - M);
l[g] = fmaf(l[g], wa, lo * wb);
m[g] = M;
#pragma unroll
for (int e = 0; e < E; ++e) {
const float oo = __shfl_xor_sync(0xffffffffu, o[g][e], off);
o[g][e] = fmaf(o[g][e], wa, oo * wb);
}
}
}
// First lane group of each warp publishes the warp's state.
if (grp == 0) {
#pragma unroll
for (int g = 0; g < G; ++g) {
#pragma unroll
for (int e = 0; e < E; ++e) sm_o[warp][g][gl * E + e] = o[g][e];
if (gl == 0) {
sm_m[warp][g] = m[g];
sm_l[warp][g] = l[g];
}
}
}
__syncthreads();
// Merge warps; write final output (single split) or fp32 partials.
for (int idx = threadIdx.x; idx < G * D; idx += NWARPS * 32) {
const int g = idx / D;
const int d = idx - g * D;
float M = NEG_INF;
#pragma unroll
for (int w = 0; w < NWARPS; ++w) M = fmaxf(M, sm_m[w][g]);
float L = 0.f, O = 0.f;
#pragma unroll
for (int w = 0; w < NWARPS; ++w) {
const float wgt = exp2f(sm_m[w][g] - M);
L = fmaf(sm_l[w][g], wgt, L);
O = fmaf(sm_o[w][g][d], wgt, O);
}
if (Sb == 1) {
out[((int64_t)b * H + kvh * G + g) * D + d] = __float2bfloat16(O / L);
} else {
// Store the split-local softmax output (normalized) in bf16 to
// halve partial traffic; merge weights come from (M, L) in fp32.
o_part[((((int64_t)b * Hkv + kvh) * S + split) * G + g) * D + d] =
__float2bfloat16(O / L);
if (d == 0) {
float* mlp = ml_part + ((((int64_t)b * Hkv + kvh) * S + split) * G + g) * 2;
mlp[0] = M;
mlp[1] = L;
}
}
}
if (Sb == 1) return;
// Semaphore: the last block of this (b, kvh) group merges all partials.
// atomicInc with val = Sb-1 wraps back to 0, so no reset pass is needed.
__threadfence();
__syncthreads();
if (threadIdx.x == 0)
sm_last = (atomicInc(&sem[b * Hkv + kvh], (unsigned)(Sb - 1)) == (unsigned)(Sb - 1));
__syncthreads();
if (!sm_last) return;
const bf16* op = o_part + ((int64_t)b * Hkv + kvh) * S * G * D;
const float* mlp = ml_part + ((int64_t)b * Hkv + kvh) * S * G * 2;
for (int idx = threadIdx.x; idx < G * D; idx += NWARPS * 32) {
const int g = idx / D;
const int d = idx - g * D;
float M = NEG_INF;
for (int s = 0; s < Sb; ++s) M = fmaxf(M, mlp[(s * G + g) * 2]);
float W = 0.f, O = 0.f;
for (int s = 0; s < Sb; ++s) {
const float w = exp2f(mlp[(s * G + g) * 2] - M) * mlp[(s * G + g) * 2 + 1];
W += w;
O = fmaf(w, __bfloat162float(op[((int64_t)s * G + g) * D + d]), O);
}
out[((int64_t)b * H + kvh * G + g) * D + d] = __float2bfloat16(O / W);
}
}
void paged_decode(at::Tensor q, at::Tensor kv, at::Tensor bt, at::Tensor sl,
at::Tensor out, at::Tensor o_part, at::Tensor ml, at::Tensor sem,
int64_t S, int64_t chunk, int64_t nwarps, int64_t pf, double qscale) {
const int H = q.size(1);
const int D = q.size(2);
const int B = q.size(0);
const int Hkv = kv.size(2);
const int G = H / Hkv;
const int maxb = bt.size(1);
auto stream = at::cuda::getCurrentCUDAStream();
dim3 grid((unsigned)S, (unsigned)Hkv, (unsigned)B);
#define LAUNCH(D_, G_, W_, PF_) \
decode_split_kernel<D_, G_, W_, PF_><<<grid, W_ * 32, 0, stream>>>( \
reinterpret_cast<const bf16*>(q.data_ptr()), \
reinterpret_cast<const bf16*>(kv.data_ptr()), \
bt.data_ptr<int>(), sl.data_ptr<int>(), \
reinterpret_cast<bf16*>(o_part.data_ptr()), ml.data_ptr<float>(), \
reinterpret_cast<unsigned*>(sem.data_ptr()), \
reinterpret_cast<bf16*>(out.data_ptr()), \
Hkv, (int)S, (int)chunk, maxb, (float)qscale)
#define PF_SWITCH(D_, G_, W_) \
do { \
if (pf == 3) LAUNCH(D_, G_, W_, 3); \
else if (pf == 4) LAUNCH(D_, G_, W_, 4); \
else if (pf == 6) LAUNCH(D_, G_, W_, 6); \
else LAUNCH(D_, G_, W_, 2); \
} while (0)
if (D == 128 && G == 4) {
if (nwarps == 4) PF_SWITCH(128, 4, 4);
else if (nwarps == 16) PF_SWITCH(128, 4, 16);
else PF_SWITCH(128, 4, 8);
} else if (D == 128 && G == 8) {
if (nwarps == 4) PF_SWITCH(128, 8, 4);
else if (nwarps == 16) PF_SWITCH(128, 8, 16);
else PF_SWITCH(128, 8, 8);
} else if (D == 64 && G == 4) {
if (nwarps == 2) PF_SWITCH(64, 4, 2);
else if (nwarps == 8) PF_SWITCH(64, 4, 8);
else if (nwarps == 16) PF_SWITCH(64, 4, 16);
else PF_SWITCH(64, 4, 4);
} else if (D == 64 && G == 8) {
if (nwarps == 8) PF_SWITCH(64, 8, 8);
else PF_SWITCH(64, 8, 4);
} else {
TORCH_CHECK(false, "unsupported (D, G) = (", D, ", ", G, ")");
}
#undef PF_SWITCH
#undef LAUNCH
}
"""
_ext = None
def _get_ext():
global _ext
if _ext is None:
from torch.utils.cpp_extension import load_inline
os.environ["TORCH_CUDA_ARCH_LIST"] = "12.0a"
_ext = load_inline(
name="paged_decode_v3",
cpp_sources=[_CPP_SRC],
cuda_sources=[_CUDA_SRC],
functions=["paged_decode"],
extra_cuda_cflags=["-O3", "--use_fast_math"],
verbose=os.environ.get("PD_VERBOSE", "0") == "1",
)
return _ext
_LOG2E = 1.4426950408889634
# Tuned launch plans: (B, Hkv, G, D, L) -> (num_splits, nwarps, prefetch_depth)
_PLANS = {
(8, 8, 4, 128, 1024): (2, 8, 2),
(32, 8, 4, 128, 2048): (1, 8, 2),
(4, 8, 8, 128, 4096): (9, 8, 2),
(16, 8, 4, 128, 1535): (4, 4, 2),
(8, 4, 4, 64, 2000): (4, 8, 6),
}
def _plan(batch, num_kv_heads, group, head_dim, seq_len):
env_s = os.environ.get("PD_S")
env_w = os.environ.get("PD_NWARPS")
env_pf = os.environ.get("PD_PF")
key = (batch, num_kv_heads, group, head_dim, seq_len)
if key in _PLANS and not (env_s or env_w or env_pf):
return _PLANS[key]
base = _PLANS.get(key)
pairs = batch * num_kv_heads
if env_s:
S = int(env_s)
elif base:
S = base[0]
else:
target = int(os.environ.get("PD_TARGET_BLOCKS", "576"))
S = max(1, -(-target // pairs))
if env_w:
nwarps = int(env_w)
elif base:
nwarps = base[1]
else:
nwarps = 8 if head_dim == 128 else 4
if env_pf:
pf = int(env_pf)
elif base:
pf = base[2]
else:
pf = 2
return S, nwarps, pf
class Model(nn.Module):
"""Single-query paged attention decode (matches reference.Model interface)."""
def __init__(self, batch, num_heads, num_kv_heads, head_dim, seq_len, page_size):
super().__init__()
assert num_heads % num_kv_heads == 0
self.batch = batch
self.num_heads = num_heads
self.num_kv_heads = num_kv_heads
self.head_dim = head_dim
self.seq_len = seq_len
self.page_size = page_size
self.group_size = num_heads // num_kv_heads
self.scale = 1.0 / math.sqrt(head_dim)
self.qscale = self.scale * _LOG2E
self.register_buffer("_dummy", torch.zeros(1, dtype=torch.bfloat16), persistent=False)
G = self.group_size
self._supported = page_size == 16 and (head_dim, G) in (
(128, 4), (128, 8), (64, 4), (64, 8),
)
S, nwarps, pf = _plan(batch, num_kv_heads, G, head_dim, seq_len)
chunk = max(16, (-(-seq_len // S) + 15) // 16 * 16)
chunk = min(chunk, 4096)
S = -(-seq_len // chunk)
self.S = S
self.chunk = chunk
self.nwarps = nwarps
self.pf = pf
if self._supported and torch.cuda.is_available():
dev = torch.device("cuda")
self._out = torch.empty(batch, num_heads, head_dim, dtype=torch.bfloat16, device=dev)
self._opart = torch.empty(
batch, num_kv_heads, S, G, head_dim, dtype=torch.bfloat16, device=dev
)
self._ml = torch.empty(batch, num_kv_heads, S, G, 2, dtype=torch.float32, device=dev)
self._sem = torch.zeros(batch, num_kv_heads, dtype=torch.int32, device=dev)
self._fn = _get_ext().paged_decode
self._rest = (self._out, self._opart, self._ml, self._sem,
S, chunk, nwarps, pf, self.qscale)
else:
self._out = None
self._fn = None
# Hot path: skip nn.Module.__call__ hook dispatch (a few us per call).
def __call__(self, query, kv_cache, block_table, seq_lens):
fn = self._fn
if fn is not None:
fn(query, kv_cache, block_table, seq_lens, *self._rest)
return self._out
return self._fallback(query, kv_cache, block_table, seq_lens)
forward = __call__
def _fallback(self, query, kv_cache, block_table, seq_lens):
B, H, D = query.shape
P = self.page_size
G = self.group_size
out = torch.empty_like(query)
for b in range(B):
L = int(seq_lens[b].item())
np_ = (L + P - 1) // P
kv = kv_cache.index_select(0, block_table[b, :np_].long())
kv = kv.reshape(np_ * P, self.num_kv_heads, 2 * D)[:L]
k = kv[..., :D].repeat_interleave(G, dim=1).float()
v = kv[..., D:].repeat_interleave(G, dim=1).float()
qf = query[b].float()
scores = torch.einsum("hd,lhd->hl", qf, k) * self.scale
probs = torch.softmax(scores, dim=-1)
out[b] = torch.einsum("hl,lhd->hd", probs, v).to(query.dtype)
return out
def get_inputs():
B, H, Hkv, D, L, P = BATCH, NUM_HEADS, NUM_KV_HEADS, HEAD_DIM, SEQ_LEN, PAGE_SIZE
pages_per_seq = (L + P - 1) // P
total_pages = max(B * pages_per_seq + 8, 64)
query = torch.randn(B, H, D, dtype=torch.bfloat16) * 0.1
kv_cache = torch.randn(total_pages, P, Hkv, 2 * D, dtype=torch.bfloat16) * 0.1
perm = torch.randperm(total_pages)[: B * pages_per_seq].reshape(B, pages_per_seq).int()
block_table = perm.contiguous()
seq_lens = torch.full((B,), L, dtype=torch.int32)
return [query, kv_cache, block_table, seq_lens]
def get_init_inputs():
return [BATCH, NUM_HEADS, NUM_KV_HEADS, HEAD_DIM, SEQ_LEN, PAGE_SIZE]
Benchmark with untuned defaults: 0.5643. Filling `_PLANS` with the sweep winners.
warning: `VIRTUAL_ENV=/home/infatoshi/benchmarks/KernelBench-Hard/.venv` does not match the project environment path `/home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo/.venv` and will be ignored; use `--active` to target the active environment instead
benchmark_event event=variant_start shape=0 variant=solution ts=2026-06-11T12:02:26.292836+00:00
benchmark_event event=variant_end shape=0 variant=solution ts=2026-06-11T12:02:26.298235+00:00 elapsed_s=0.005 ms=0.032544
shape=0 variant=solution tflops=4.124 gbps=1035.076 ms=0.033
shape=0 solution_peak_fraction=0.5750
benchmark_event event=variant_start shape=1 variant=solution ts=2026-06-11T12:02:27.889554+00:00
benchmark_event event=variant_end shape=1 variant=solution ts=2026-06-11T12:02:27.899205+00:00 elapsed_s=0.010 ms=0.181696
shape=1 variant=solution tflops=5.910 gbps=1480.273 ms=0.182
shape=1 solution_peak_fraction=0.8224
benchmark_event event=variant_start shape=2 variant=solution ts=2026-06-11T12:02:28.298316+00:00
benchmark_event event=variant_end shape=2 variant=solution ts=2026-06-11T12:02:28.303154+00:00 elapsed_s=0.005 ms=0.059376
shape=2 variant=solution tflops=9.042 gbps=1132.443 ms=0.059
shape=2 solution_peak_fraction=0.6291
benchmark_event event=variant_start shape=3 variant=solution ts=2026-06-11T12:02:28.897113+00:00
benchmark_event event=variant_end shape=3 variant=solution ts=2026-06-11T12:02:28.902655+00:00 elapsed_s=0.006 ms=0.075632
shape=3 variant=solution tflops=5.320 gbps=1333.561 ms=0.076
shape=3 solution_peak_fraction=0.7409
benchmark_event event=variant_start shape=4 variant=solution ts=2026-06-11T12:02:28.999230+00:00
benchmark_event event=variant_end shape=4 variant=solution ts=2026-06-11T12:02:29.002552+00:00 elapsed_s=0.003 ms=0.020272
shape=4 variant=solution tflops=3.233 gbps=809.825 ms=0.020
shape=4 solution_peak_fraction=0.4499
peak_fraction: 0.6299
RESULT: OK
warning: `VIRTUAL_ENV=/home/infatoshi/benchmarks/KernelBench-Hard/.venv` does not match the project environment path `/home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo/.venv` and will be ignored; use `--active` to target the active environment instead
warning: Ignoring existing virtual environment linked to non-existent Python interpreter: /home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo/.venv/bin/python3 -> python
Using CPython 3.11.15
Removed virtual environment at: /home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo/.venv
Creating virtual environment at: /home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo/.venv
Building kernelbench-hard @ file:///home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo
Built kernelbench-hard @ file:///home/infatoshi/benchmarks/KernelBench-Hard/outputs/runs/20260611_050147_claude_claude-fable-5_03_paged_attention/repo
Installed 56 packages in 71ms
PASS
{
"run_id": "20260611_050147_claude_claude-fable-5_03_paged_attention",
"run_group": "",
"problem": "03_paged_attention",
"harness": "claude",
"model": "claude-fable-5",
"reasoning_effort": "max",
"started_at": "2026-06-11T05:01:47-06:00",
"harness_finished_at": "2026-06-11T06:01:48-06:00",
"finished_at": "2026-06-11T06:02:29-06:00",
"start_epoch": 1781175707,
"harness_end_epoch": 1781179308,
"end_epoch": 1781179349,
"has_solution": true,
"correct": true,
"failure_reason": "pass",
"retryable_infra_failure": false,
"minimum_useful_output_tokens": 5000,
"peak_fraction": 0.6299,
"template_mutated": false,
"elapsed_seconds": 3601,
"total_elapsed_seconds": 3642,
"check_elapsed_seconds": 37,
"benchmark_elapsed_seconds": 4,
"check_timeout_seconds": 180,
"benchmark_timeout_seconds": 1800,
"check_exit_code": 0,
"benchmark_exit_code": 0,
"harness_exit_code": 124,
"session_complete": false,
"agent_cuda_disabled": false,
"agent_container": true,
"agent_container_image": "nvcr.io/nvidia/tensorrt-llm/release:latest",
"agent_container_network": "bridge",
"gpu_queue_mode": "agent_container_native_profiling_path_wrapper_gpu_lock",
"output_tokens_per_second": 2.22299361288531,
"usage": {"input_tokens": 324, "output_tokens": 8005, "cache_read_tokens": 14189559, "cache_creation_tokens": 771262, "reasoning_tokens": null, "total_cost_usd": null}
}
timeline (295 events)
system — init
session start cwd=/workspace/problems/03_paged_attention model=claude-fable-5 permissions=bypassPermissions
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I'll start by exploring the workspace to understand the problem setup.
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stdout (459 chars)
total 44
drwxrwxr-x 2 1002 1002 4096 Jun 11 11:01 .
drwxrwxr-x 3 1002 1002 4096 Jun 11 11:01 ..
-rw-rw-r-- 1 1002 1002 2585 Apr 27 09:21 PROMPT.txt
-rw-rw-r-- 1 1002 1002 5387 Jun 1 21:05 benchmark.py
-rw-rw-r-- 1 1002 1002 3841 Jun 2 01:08 check.py
-rw-rw-r-- 1 1002 1002 2030 Apr 26 04:19 problem.yaml
-rw-rw-r-- 1 1002 1002 5151 Apr 26 04:19 reference.py
-rw-rw-r-- 1 1002 1002 933 Apr 26 04:19 shapes.py
-rw-rw-r-- 1 1002 1002 2819 Apr 26 04:24 sota.py
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1 """Naive PyTorch paged-attention decode reference (correctness oracle, not SOTA).
2
3 Single-query decode: each batch element has a query of shape (num_heads, head_dim)
4 and attends over a KV cache of `seq_len[b]` tokens stored as fixed-size pages in
5 a global pool. Pages for batch element b are listed in `block_table[b]`.
6
7 The reference performs the slow path:
8 1. Gather pages -> contiguous (seq_len, num_kv_heads, head_dim) per batch element.
9 2. Repeat KV heads for grouped-query (broadcast num_kv_heads -> num_heads).
10 3. Manual softmax(QK^T / sqrt(d)) @ V in fp32, cast back to bf16.
11
12 This avoids torch.nn.functional.scaled_dot_product_attention (which is on the
13 forbidden list) so the agent cannot dispatch through SDPA either.
14 """
15 import math
16
17 import torch
18 import torch.nn as nn
19
20 OP_TYPE = "attention"
21 SUPPORTED_PRECISIONS = ["bf16"]
22 HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]
23
24
25 # --- Shape knobs (overridden by check.py / benchmark.py from shapes.py) ----
26 BATCH = 8
27 NUM_HEADS = 32
28 NUM_KV_HEADS = 8
29 HEAD_DIM = 128
30 SEQ_LEN = 1024
31 PAGE_SIZE = 16
32
33
34 class Model(nn.Module):
35 """Single-query paged attention decode.
36
37 Forward inputs (all on device):
38 query: (batch, num_heads, head_dim) bf16
39 kv_cache: (num_blocks, page_size, num_kv_heads, head_dim * 2)
40 Layout: last dim packs [K | V] so a single gather pulls both.
4
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1 """Correctness runner for paged-attention decode.
2
3 Runs solution.Model vs reference.Model across all shapes in shapes.py, 3 seeds
4 each, with per-dtype atol/rtol. Also rejects forbidden ops by grep.
5 """
6 import re
7 import sys
8 from pathlib import Path
9
10 import torch
11 import yaml
12
13 REPO_ROOT = Path(__file__).resolve().parents[2]
14 sys.path.insert(0, str(REPO_ROOT))
15
16 from src.eval.correctness import check_correctness # noqa: E402
17 from src.eval.numeric_stress import ( # noqa: E402
18 numeric_stress_cases,
19 numeric_stress_context,
20 tolerance_for_case,
21 )
22
23
24 def _apply_shape(reference, shape: dict) -> None:
25 reference.BATCH = shape["batch"]
26 reference.NUM_HEADS = shape["num_heads"]
27 reference.NUM_KV_HEADS = shape["num_kv_heads"]
28 reference.HEAD_DIM = shape["head_dim"]
29 reference.SEQ_LEN = shape["seq_len"]
30 reference.PAGE_SIZE = shape["page_size"]
31
32
33 def main():
34 try:
35 import reference
36 import shapes
37 import solution
38 except Exception as e:
39 print(f"FAIL: import error: {e}")
40 sys.exit(1)
41
42 problem_yaml = Path("problem.yaml")
43 meta = yaml.safe_load(problem_yaml.read_text()) if problem_yaml.exists() else {}
44
45 sol_src = Path("solution.py").read_text() if Path("solution.py").exists() else ""
46 for forbidden in meta.get("forbidden", []):
47 pat = re.escape(forbidden)
48 if re.se
... (2701 more chars)
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1 """Roofline benchmark for paged-attention decode.
2
3 For each shape: times the agent's solution first. Optional eager, compiled,
4 and SOTA diagnostics are enabled with KBH_BENCHMARK_BASELINES=1. Reports achieved TFLOPS, GB/s, and peak_fraction.
5
6 Decode is memory-bound, so peak_fraction is computed from achieved GB/s vs
7 the GPU's peak DRAM bandwidth.
8 """
9 import sys
10 from math import exp, log
11 from pathlib import Path
12
13 import torch
14 import yaml
15
16 REPO_ROOT = Path(__file__).resolve().parents[2]
17 sys.path.insert(0, str(REPO_ROOT))
18
19 from src.eval.roofline import compute_gbps, compute_tflops, peak_fraction # noqa: E402
20 from src.eval.timing import benchmark_baselines_enabled, time_variant # noqa: E402
21 from src.hardware import get as get_hw # noqa: E402
22
23
24 def _eval_formula(expr: str, vars: dict) -> float:
25 return float(eval(expr, {"__builtins__": {}}, vars))
26
27
28 def _apply_shape(reference, shape: dict) -> None:
29 reference.BATCH = shape["batch"]
30 reference.NUM_HEADS = shape["num_heads"]
31 reference.NUM_KV_HEADS = shape["num_kv_heads"]
32 reference.HEAD_DIM = shape["head_dim"]
33 reference.SEQ_LEN = shape["seq_len"]
34 reference.PAGE_SIZE = shape["page_size"]
35
36
37 def main():
38 import reference
39 import shapes
40 import solution
41
42 meta = yaml.safe_load(Path("problem.yaml").read_text())
43 hw = get_hw(meta["hardware"][0])
44 peak_tflops = hw.peak_tflop
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stdout (981 chars)
1 """Shape sweep for paged attention decode.
2
3 Mix targets:
4 - small batch / long context (Llama-3 8B-style decode)
5 - large batch / medium context (server batched decode)
6 - GQA wide ratio (Llama-3 70B: 64 heads / 8 kv-heads)
7 - non-power-of-2 seq_len (forces predicated tail handling)
8 - head_dim=64 small-head case
9 """
10
11 SHAPES = [
12 # (B, H, Hkv, D, L, P)
13 {"batch": 8, "num_heads": 32, "num_kv_heads": 8, "head_dim": 128, "seq_len": 1024, "page_size": 16},
14 {"batch": 32, "num_heads": 32, "num_kv_heads": 8, "head_dim": 128, "seq_len": 2048, "page_size": 16},
15 {"batch": 4, "num_heads": 64, "num_kv_heads": 8, "head_dim": 128, "seq_len": 4096, "page_size": 16},
16 {"batch": 16, "num_heads": 32, "num_kv_heads": 8, "head_dim": 128, "seq_len": 1535, "page_size": 16}, # non-pow2
17 {"batch": 8, "num_heads": 16, "num_kv_heads": 4, "head_dim": 64, "seq_len": 2000, "page_size": 16}, # small-D, non-pow2
18 ]
19
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1 """SOTA reference for paged-attention decode.
2
3 Tries, in order:
4 1. FlashInfer's BatchDecodeWithPagedKVCacheWrapper (preferred -- portable,
5 supports SM120, GQA, arbitrary head_dim).
6 2. vLLM's paged_attention_v2 CUDA op (requires its KV-cache layout, more
7 finicky; we adapt the layout on the fly when possible).
8
9 If neither is importable, is_available() returns False and the benchmark just
10 reports eager + compiled + solution.
11
12 Agents are FORBIDDEN from importing these in solution.py (see problem.yaml).
13 This file is only for the benchmark's reference line.
14 """
15 from __future__ import annotations
16
17 import torch
18
19
20 def _try_flashinfer(
21 query: torch.Tensor,
22 kv_cache: torch.Tensor,
23 block_table: torch.Tensor,
24 seq_lens: torch.Tensor,
25 num_kv_heads: int,
26 head_dim: int,
27 page_size: int,
28 ) -> torch.Tensor | None:
29 try:
30 import flashinfer # noqa: F401
31 from flashinfer.decode import BatchDecodeWithPagedKVCacheWrapper
32 except Exception:
33 return None
34
35 B, H, D = query.shape
36 # FlashInfer expects K and V as separate (num_blocks, page_size, num_kv_heads, head_dim) tensors.
37 # Our reference packs [K|V] on the last dim -- split here.
38 k_cache = kv_cache[..., :D].contiguous()
39 v_cache = kv_cache[..., D:].contiguous()
40
41 workspace = torch.empty(128 * 1024 * 1024, dtype=torch.uint8, device=query.device)
42
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1 name: 03_paged_attention
2 display_name: "Paged Attention Decode"
3 precision: bf16
4 regime: memory # decode is bandwidth-bound (KV cache streamed once per token)
5
6 # Effective FLOPs per call: QK^T + softmax*V across all batches/heads/seq.
7 # Sum-formula evaluated per-shape; the benchmark substitutes batch/num_heads/etc.
8 # 2 * B * H * L * D for QK^T plus 2 * B * H * L * D for AV => 4 * B * H * L * D
9 flops_formula: "4 * batch * num_heads * seq_len * head_dim"
10
11 # Bytes moved (the real bottleneck): the KV cache must be streamed end-to-end.
12 # K and V each: batch * seq_len * num_kv_heads * head_dim * 2 bytes (bf16)
13 # Q: batch * num_heads * head_dim * 2 (negligible vs KV)
14 # Out: same as Q
15 # So total ~ 2 * (B * L * Hkv * D * 2) + small.
16 bytes_formula: "2 * batch * seq_len * num_kv_heads * head_dim * 2 + batch * num_heads * head_dim * 2 * 2"
17
18 hardware: [RTX_PRO_6000]
19 peak_tflops_key: bf16 # informational; regime=memory uses bandwidth
20 peak_bandwidth_key: dram # 1.8 TB/s GDDR7 on RTX PRO 6000 Blackwell
21
22 tolerance:
23 bfloat16: 0.02
24 float16: 0.02
25
26 # Forbidden ops -- using any of these in solution.py fails correctness post-hoc.
27 # vllm.attention / flashinfer.batch_decode_with_paged_kv_cache: dispatching to
28 # the SOTA library is the trivial cheat. SDPA is also banned because the agent
29 # could gather pages then call SDPA and inherit FlashAttention "for free".
30 forbidden:
31 - "vllm.attenti
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stdout (199 chars)
problems
pyproject.toml
src
uv.lock
__init__.py
__pycache__
eval
hardware
harness
kbh
sandbox
viewer
__init__.py
__pycache__
correctness.py
numeric_stress.py
report.py
roofline.py
shapes.py
timing.py
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1 """Per-dtype correctness tolerance.
2
3 Stanford's KernelBench uses 1e-4 atol/rtol for fp32 and 1e-2 for fp16/bf16.
4 We extend to fp8 (0.1, permissive) and int (exact).
5 """
6 from __future__ import annotations
7
8 import torch
9
10 DEFAULT_TOLERANCE = {
11 torch.float32: {"atol": 1e-4, "rtol": 1e-4},
12 torch.float16: {"atol": 1e-2, "rtol": 1e-2},
13 torch.bfloat16: {"atol": 1e-2, "rtol": 1e-2},
14 torch.float8_e4m3fn: {"atol": 1e-1, "rtol": 1e-1},
15 torch.float8_e5m2: {"atol": 1e-1, "rtol": 1e-1},
16 torch.int8: {"atol": 0, "rtol": 0},
17 torch.int32: {"atol": 0, "rtol": 0},
18 torch.int64: {"atol": 0, "rtol": 0},
19 }
20
21
22 def _coerce_float(x):
23 """Accept int/float/str scientific-notation as float; pass through dicts."""
24 if isinstance(x, (int, float)):
25 return float(x)
26 if isinstance(x, str):
27 try:
28 return float(x)
29 except ValueError:
30 return x
31 return x
32
33
34 def tolerance_for_dtype(dtype: torch.dtype, override: dict | None = None) -> dict:
35 """Lookup atol/rtol for a given dtype, with optional per-problem override.
36
37 The override dict is keyed by str(dtype). Values may be:
38 - a single number (or a string parseable as float, e.g. "5e-2") -> used
39 as both atol and rtol
40 - a dict {"atol": ..., "rtol": ...} -> used directly, with values coerced
41 """
42 # Accept several spellings of the same dty
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1 """Numeric distribution stress cases for correctness checks.
2
3 These cases are not hidden shapes. They rerun the same shape/seed validation
4 under a few scale regimes that catch kernels that only work for the nominal
5 N(0, 1)-ish inputs.
6 """
7 from __future__ import annotations
8
9 import os
10 from collections.abc import Iterator, Mapping, Sequence
11 from contextlib import contextmanager
12 from dataclasses import dataclass, field
13
14 import torch
15
16 ToleranceOverride = Mapping[str, float | Mapping[str, float]]
17
18
19 @dataclass(frozen=True)
20 class NumericStressCase:
21 name: str
22 input_scales: Mapping[int, float] = field(default_factory=dict)
23 state_scales: Mapping[str, float] = field(default_factory=dict)
24 tolerance: ToleranceOverride | None = None
25
26
27 NOMINAL_CASE = NumericStressCase("nominal")
28
29 _SMALL_BF16 = {"bfloat16": {"atol": 1e-4, "rtol": 5e-2}}
30 _MED_BF16 = {"bfloat16": {"atol": 5e-4, "rtol": 5e-2}}
31 _LARGE_BF16 = {"bfloat16": {"atol": 2e-1, "rtol": 5e-2}}
32 _TINY_FP32 = {"float32": {"atol": 1e-7, "rtol": 1e-4}}
33 _LARGE_FP32 = {"float32": {"atol": 1e-1, "rtol": 1e-4}}
34
35 _CASES: dict[str, tuple[NumericStressCase, ...]] = {
36 "01_fp8_gemm": (
37 NumericStressCase("small_input", input_scales={0: 1e-3}, tolerance=_SMALL_BF16),
38 NumericStressCase("large_input", input_scales={0: 64.0}, tolerance=_LARGE_BF16),
39 NumericStressCase(
40 "small_weight",
41
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1 """Centralized GPU timing for benchmark.py files.
2
3 All problems' benchmark.py should call `time_fn` from here so we have one
4 implementation of warmup, L2 flush, and CUDA event capture to maintain.
5
6 Methodology:
7 - 10 warmup calls absorb Triton autotune (typical ~7 configs) and
8 torch.compile reduce-overhead CUDA-graph capture.
9 - Between each timed call, `_l2_flush()` writes 128 MB to evict L2
10 (Blackwell L2 is 96 MB; we want any prior L2 contents flushed so
11 we measure HBM-load bandwidth, not L2-cached bandwidth).
12 - GPU timing via cuda.Event with synchronize() AFTER record() but
13 BEFORE elapsed_time() — the canonical NVIDIA pattern.
14 - Reported value is the median of `iters` trials, robust to outliers.
15
16 Notes / known biases not addressed here:
17 - torch.compile(mode="reduce-overhead") gets CUDA graphs which eliminate
18 launch overhead. Custom Triton/CUDA kernels do NOT get this treatment.
19 On small shapes where launch overhead matters, this gives compile an
20 artificial advantage. We accept this as the cost of using the agreed
21 "compiled" baseline policy.
22 - cuBLAS / cuDNN allocate workspaces on first call. 10 warmup absorbs.
23 - Median over a fairly small number of trials (default 30) is fine for
24 headline numbers but won't catch bimodal distributions. Use --extra
25 instrumentation if you ever care.
26 """
27 from __future__ import annotations
28
29 import os
30 import re
31
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I have the full picture now. Let me check the environment (GPU, toolchain) and the hardware spec used for scoring.
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stdout (1791 chars) — TRUNCATED
Thu Jun 11 11:07:01 2026
+-----------------------------------------------------------------------------------------+
| NVIDIA-SMI 610.43.02 KMD Version: 610.43.02 CUDA UMD Version: 13.3 |
+-----------------------------------------+------------------------+----------------------+
| GPU Name Persistence-M | Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap | Memory-Usage | GPU-Util Compute M. |
| | | MIG M. |
|=========================================+========================+======================|
| 0 NVIDIA RTX PRO 6000 Blac... On | 00000000:01:00.0 Off | Off |
| 30% 37C P0 88W / 600W | 15MiB / 97887MiB | 0% Default |
| | | N/A |
+-----------------------------------------+------------------------+----------------------+
+-----------------------------------------------------------------------------------------+
| Processes: |
| GPU GI CI PID Type Process name GPU Memory |
| ID ID Usage |
|======================================================================================
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subagent · 0 events · 0 tools
tool
stdout (656 chars)
Using CPython 3.11.15
Creating virtual environment at: /workspace/.venv
Building kernelbench-hard @ file:///workspace
Built kernelbench-hard @ file:///workspace
warning: Failed to hardlink files; falling back to full copy. This may lead to degraded performance.
If the cache and target directories are on different filesystems, hardlinking may not be supported.
If this is intentional, set `export UV_LINK_MODE=copy` or use `--link-mode=copy` to suppress this warning.
Installed 56 packages in 1.30s
torch 2.11.0+cu130 cuda 13.0
device NVIDIA RTX PRO 6000 Blackwell Workstation Edition (12, 0)
triton 3.6.0
sm count 188
L2 128 MB
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SM120, 188 SMs, 128 MB L2, torch 2.11 + CUDA 13. Let me check the scoring peak bandwidth and verify the reference runs.
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"""Hardware peak-throughput lookup tables."""
from src.hardware.m4_max import M4_MAX
from src.hardware.rtx_pro_6000 import RTX_PRO_6000
TARGETS = {
"RTX_PRO_6000": RTX_PRO_6000,
"M4_MAX": M4_MAX,
}
def get(name: str):
if name not in TARGETS:
raise ValueError(f"Unknown hardware {name!r}; available: {list(TARGETS)}")
return TARGETS[name]
"""Apple M4 Max — unified memory, 16-core GPU, Metal 3."""
from src.hardware.rtx_pro_6000 import HardwareTarget
M4_MAX = HardwareTarget(
name="Apple M4 Max",
sm="metal3",
vram_gb=36, # unified
peak_bandwidth_gb_s=546.0,
peak_tflops_dense={
# Apple doesn't publish formal TFLOPS numbers the way NVIDIA does.
# These are community estimates from chip-level benchmarks.
"fp32": 17.0,
"fp16": 34.0,
"bf16": 34.0,
"int8": 68.0,
},
)
"""RTX PRO 6000 Blackwell Workstation — SM120, consumer-lineage Blackwell.
Peak tensor-core throughputs are dense-matrix advertised peaks. Actual kernels
will see 60-85% of peak on well-tuned code.
"""
from dataclasses import dataclass
@dataclass(frozen=True)
class HardwareTarget:
name: str
sm: str
vram_gb: int
peak_bandwidth_gb_s: float # DRAM
peak_tflops_dense: dict[str, float] # dtype -> TFLOPS
RTX_PRO_6000 = HardwareTarget(
name="RTX PRO 6000 Blackwell Workstation",
sm="sm_120a",
vram_gb=96,
peak_bandwidth_gb_s=1800.0,
peak_tflops_dense={
"fp4": 800.0,
"nvfp4"
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stdout (86 chars)
Task #1 created successfully: Write v1 CUDA split-K paged decode kernel in solution.py
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stdout (60 chars)
Task #2 created successfully: Pass check.py for all 5 shapes
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stdout (73 chars)
Task #3 created successfully: Benchmark and iterate on bandwidth fraction
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Now writing the v1 kernel.
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stdout (146 chars)
File created successfully at: /workspace/problems/03_paged_attention/solution.py (file state is current in your context — no need to Read it back)
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Now let me smoke-test the build and a single shape before running the full check.
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stdout (1710 chars) — TRUNCATED
[1/3] c++ -MMD -MF main.o.d -DTORCH_EXTENSION_NAME=paged_decode_v1 -DTORCH_API_INCLUDE_EXTENSION_H -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include/torch/csrc/api/include -isystem /usr/local/cuda-host/include -isystem /uv-cache/python/cpython-3.11.15-linux-x86_64-gnu/include/python3.11 -fPIC -std=c++17 -c /home/agent/.cache/torch_extensions/py311_cu130/paged_decode_v1/main.cpp -o main.o
[2/3] /usr/local/cuda-host/bin/nvcc -MD -MF cuda.cuda.o.d -DTORCH_EXTENSION_NAME=paged_decode_v1 -DTORCH_API_INCLUDE_EXTENSION_H -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include/torch/csrc/api/include -isystem /usr/local/cuda-host/include -isystem /uv-cache/python/cpython-3.11.15-linux-x86_64-gnu/include/python3.11 -D__CUDA_NO_HALF_OPERATORS__ -D__CUDA_NO_HALF_CONVERSIONS__ -D__CUDA_NO_BFLOAT16_CONVERSIONS__ -D__CUDA_NO_HALF2_OPERATORS__ --expt-relaxed-constexpr -gencode=arch=compute_100,code=sm_100 -gencode=arch=compute_120,code=compute_120 -gencode=arch=compute_120,code=sm_120 -gencode=arch=compute_75,code=sm_75 -gencode=arch=compute_80,code=sm_80 -gencode=arch=compute_86,code=sm_86 -gencode=arch=compute_90,code=sm_90 --compiler-options '-fPIC' -O3 --use_fast_math -std=c++17 -c /home/agent/.cache/torch_extensions/py311_cu130/paged_decode_v1/cuda.cu -o cuda.cuda.o
[3/3] c++ main.o cuda.cuda.o -shared -L/workspace/.v
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stdout (156 chars)
The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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subagent · 0 events · 0 tools
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stdout (524 chars)
shape=0 variant=solution tflops=3.638 gbps=912.985 ms=0.037
shape=0 solution_peak_fraction=0.5072
shape=1 variant=solution tflops=5.254 gbps=1316.159 ms=0.204
shape=1 solution_peak_fraction=0.7312
shape=2 variant=solution tflops=6.776 gbps=848.646 ms=0.079
shape=2 solution_peak_fraction=0.4715
shape=3 variant=solution tflops=5.133 gbps=1286.478 ms=0.078
shape=3 solution_peak_fraction=0.7147
shape=4 variant=solution tflops=2.880 gbps=721.553 ms=0.023
shape=4 solution_peak_fraction=0.4009
peak_fraction: 0.5495
RESULT: OK
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stdout (147 chars)
File created successfully at: /workspace/problems/03_paged_attention/bench_dev.py (file state is current in your context — no need to Read it back)
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stdout (1483 chars)
_warn_once(
shape=0 ms= 36.7us gbps= 918.2 frac=0.5101 S=8 chunk=128 nwarps=8
24.0us x1 void decode_split_kernel<128, 4, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
2.4us x1 void reduce_kernel<128, 4>(float const*, float const*, int const*, __nv_bfloat16*, int, in
shape=1 ms= 204.8us gbps= 1313.2 frac=0.7295 S=3 chunk=688 nwarps=8
181.0us x1 void decode_split_kernel<128, 4, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
2.1us x1 void reduce_kernel<128, 4>(float const*, float const*, int const*, __nv_bfloat16*, int, in
shape=2 ms= 80.7us gbps= 833.7 frac=0.4631 S=18 chunk=240 nwarps=8
54.7us x1 void decode_split_kernel<128, 8, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
7.2us x1 void reduce_kernel<128, 8>(float const*, float const*, int const*, __nv_bfloat16*, int, in
shape=3 ms= 79.8us gbps= 1264.5 frac=0.7025 S=5 chunk=320 nwarps=8
64.5us x1 void decode_split_kernel<128, 4, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
2.3us x1 void reduce_kernel<128, 4>(float const*, float const*, int const*, __nv_bfloat16*, int, in
shape=4 ms= 24.0us gbps= 684.9 frac=0.3805 S=18 chunk=112 nwarps=4
8.9us x1 void decode_split_kernel<64, 4, 4>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*,
2.9us x1 void reduce_kernel<64, 4>(float const*, float const*, int const*, __nv_bfloat16*, int, int
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stdout (79 chars)
/kbh/bin/ncu
/kbh/bin/nsys
Version 2025.2.1.0 (build 35987062) (public-release)
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stdout (146 chars)
File created successfully at: /workspace/problems/03_paged_attention/prof_one.py (file state is current in your context — no need to Read it back)
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stdout (4431 chars) — TRUNCATED
==PROF== Profiling "decode_split_kernel": 0%....50%....100% - 9 passes
==PROF== Profiling "reduce_kernel": 0%....50%....100% - 9 passes
==PROF== Profiling "decode_split_kernel": 0%....50%....100% - 9 passes
==PROF== Profiling "reduce_kernel": 0%....50%....100% - 9 passes
void decode_split_kernel<128, 4, 8>(const __nv_bfloat16 *, const __nv_bfloat16 *, const int *, const int *, float *, float *, __nv_bfloat16 *, int, int, int, int, float) (8, 8, 8)x(256, 1, 1), Context 1, Stream 7, Device 0, CC 12.0
Metric Name Metric Unit Metric Value
dram__bytes_read.sum (!) n/a
dram__bytes_write.sum (!) n/a
dram__throughput.avg.pct_of_peak_sustained_elapsed % 75.28
gpu__time_duration.sum us 26.18
launch__occupancy_limit_registers block 2
launch__occupancy_limit_shared_mem block 5
launch__registers_per_thread register/thread 117
sm__throughput.avg.pct_of_peak_sustained_elapsed % 16.16
sm__warps_active.avg.pct_of_peak_sustained_active % 31.28
void reduce_kernel<128, 4>(const float *, const float *, const int *, __nv_bfloat16 *, int, int, int) (8, 8, 1)x(256, 1, 1), Context 1, Stream 7, Device
... (2931 more chars)
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stdout (156 chars)
The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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stdout (921 chars)
PASS
shape=0 ms= 36.5us gbps= 922.6 frac=0.5125 S=8 chunk=128 nwarps=8
25.2us x1 void decode_split_kernel<128, 4, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
shape=1 ms= 205.0us gbps= 1311.9 frac=0.7289 S=3 chunk=688 nwarps=8
179.6us x1 void decode_split_kernel<128, 4, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
shape=2 ms= 73.2us gbps= 919.2 frac=0.5107 S=18 chunk=240 nwarps=8
57.2us x1 void decode_split_kernel<128, 8, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
shape=3 ms= 87.7us gbps= 1149.7 frac=0.6387 S=5 chunk=320 nwarps=8
66.2us x1 void decode_split_kernel<128, 4, 8>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*
shape=4 ms= 23.8us gbps= 689.5 frac=0.3831 S=18 chunk=112 nwarps=4
10.8us x1 void decode_split_kernel<64, 4, 4>(__nv_bfloat16 const*, __nv_bfloat16 const*, int const*,
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stdout (1756 chars) — TRUNCATED
void decode_split_kernel<128, 4, 8>(const __nv_bfloat16 *, const __nv_bfloat16 *, const int *, const int *, float *, float *, unsigned int *, __nv_bfloat16 *, int, int, int, int, float) (8, 8, 8)x(256, 1, 1), Context 1, Stream 7, Device 0, CC 12.0
dram__throughput.avg.pct_of_peak_sustained_elapsed % 68.73
gpu__time_duration.sum us 28.70
launch__registers_per_thread register/thread 118
sm__warps_active.avg.pct_of_peak_sustained_active % 31.12
void decode_split_kernel<128, 4, 8>(const __nv_bfloat16 *, const __nv_bfloat16 *, const int *, const int *, float *, float *, unsigned int *, __nv_bfloat16 *, int, int, int, int, float) (5, 8, 16)x(256, 1, 1), Context 1, Stream 7, Device 0, CC 12.0
dram__throughput.avg.pct_of_peak_sustained_elapsed % 86.84
gpu__time_duration.sum us 67.90
launch__registers_per_thread register/thread 118
sm__warps_active.avg.pct_of_peak_sustained_active % 30.41
void decode_split_kernel<64, 4, 4>(const __nv_bfloat16 *, const __nv_bfloat16 *, const int *, const int *, float *, float *, unsigned int *, __nv_bfloat16 *, int, int, int, int, float) (18, 4, 8)x(128, 1, 1), Context 1, Stream 7, Device 0, CC 12.0
dram__throughput.avg.pct_of_peak_sustained_elapsed % 5
... (256 more chars)
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stdout (154 chars)
File created successfully at: /workspace/problems/03_paged_attention/microbench_loads.py (file state is current in your context — no need to Read it back)
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stdout (2698 chars) — TRUNCATED
^^^^^^^^^^^^^
File "/workspace/.venv/lib/python3.11/site-packages/torch/utils/cpp_extension.py", line 2268, in _jit_compile
_write_ninja_file_and_build_library(
File "/workspace/.venv/lib/python3.11/site-packages/torch/utils/cpp_extension.py", line 2429, in _write_ninja_file_and_build_library
_run_ninja_build(
File "/workspace/.venv/lib/python3.11/site-packages/torch/utils/cpp_extension.py", line 2791, in _run_ninja_build
raise RuntimeError(message) from e
RuntimeError: Error building extension 'mb_loads': [1/3] c++ -MMD -MF main.o.d -DTORCH_EXTENSION_NAME=mb_loads -DTORCH_API_INCLUDE_EXTENSION_H -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include/torch/csrc/api/include -isystem /usr/local/cuda-host/include -isystem /uv-cache/python/cpython-3.11.15-linux-x86_64-gnu/include/python3.11 -fPIC -std=c++17 -c /home/agent/.cache/torch_extensions/py311_cu130/mb_loads/main.cpp -o main.o
[2/3] /usr/local/cuda-host/bin/nvcc -MD -MF cuda.cuda.o.d -DTORCH_EXTENSION_NAME=mb_loads -DTORCH_API_INCLUDE_EXTENSION_H -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include -isystem /workspace/.venv/lib/python3.11/site-packages/torch/include/torch/csrc/api/include -isystem /usr/local/cuda-host/include -isystem /uv-cache/python/cpython-3.11.15-linux-x86_64-gnu/include/python3.11 -D__CUDA_NO_HALF_OPERATORS__ -D__CUDA_NO_HALF_CONVERSIONS__ -D__CUDA_NO_BFLOAT16_CONVERSIONS__ -D__CUDA_N
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stdout (804 chars)
I cannot provide the specific information you've requested based on the content above. While the document table of contents references "Cache Eviction Priority Hints" (section 9.7.9.2) and mentions `createpolicy` in the instruction list (9.7.9.19), the actual detailed syntax, valid priority combinations, and parameter specifications for the `createpolicy` instruction are not included in the provided excerpt.
The document appears to be truncated before reaching the complete instruction descriptions. To access the precise syntax for `createpolicy.fractional`, its valid primary and secondary priorities, and clarification on whether `ld.global` supports direct `.L2::no_allocate` qualifiers, you would need to consult the full PTX ISA 9.3 documentation or the complete sections 9.7.9.2 and 9.7.9.19.
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stdout (3512 chars) — TRUNCATED
Web search results for query: "PTX createpolicy.fractional L2 no_allocate primary priority syntax cache_hint"
Links: [{"title":"Nvcc 13.1 ptxas codegen bug: createpolicy.fractional dropped on sm_90 - CUDA NVCC Compiler - NVIDIA Developer Forums","url":"https://forums.developer.nvidia.com/t/nvcc-13-1-ptxas-codegen-bug-createpolicy-fractional-dropped-on-sm-90/368663"},{"title":"PTX createpolicy instruction compile failure - CUDA NVCC Compiler - NVIDIA Developer Forums","url":"https://forums.developer.nvidia.com/t/ptx-createpolicy-instruction-compile-failure/333913"},{"title":"PTX ISA Release 8.8 NVIDIA Corporation May 31, 2025","url":"https://docs.nvidia.com/cuda/pdf/ptx_isa_8.8.pdf"},{"title":"How to use createpolicy ptx instruction well in CUDA? Are there any practical examples as reference? - CUDA Programming and Performance - NVIDIA Developer Forums","url":"https://forums.developer.nvidia.com/t/how-to-use-createpolicy-ptx-instruction-well-in-cuda-are-there-any-practical-examples-as-reference/247592"},{"title":"User Guide for NVPTX Back-end — LLVM 23.0.0git documentation","url":"https://llvm.org/docs/NVPTXUsage.html"},{"title":"Setting eviction policy of store command does not affect underlying PTX instruction · Issue #1728 · triton-lang/triton","url":"https://github.com/triton-lang/triton/issues/1728"},{"title":"PTX ISA Release 8.7 NVIDIA Corporation Feb 27, 2025","url":"https://docs.nvidia.com/cuda/pdf/ptx_isa_8.7.pdf"},{"title":"DeepSeek and DeepEP — Understanding DeepSe
... (2012 more chars)
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stdout (131 chars)
-rw-r--r-- 1 1002 1002 20058950 Jun 11 11:29 ptx_isa.pdf
no pdftotext
Shell cwd was reset to /workspace/problems/03_paged_attention
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stdout (70 chars)
no pypdf
Shell cwd was reset to /workspace/problems/03_paged_attention
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The Read tool can read PDFs, but faster: ptxas is ground truth. Let me compile-test candidate syntaxes directly.
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stdout (1543 chars) — TRUNCATED
VARIANT 1:
VARIANT 2: ptxas /tmp/tmpxft_0000075f_00000000-7_polytest.compute_120.ptx, line 27; error : Argument 2 of instruction 'createpolicy.fractional': value '0.000000' out of range, expected to be in range (0.000000 .. 1.000000] ptxas /tmp/tmpxft_0000075f_00000000-7_polytest.compute_120.ptx, line 27; error : Unsupported modifier '.no_allocate' as secondary_priority for instruction 'createpolicy.fractional'
VARIANT 3: ptxas /tmp/tmpxft_00000776_00000000-7_polytest.compute_120.ptx, line 27; error : Argument 2 of instruction 'createpolicy.fractional': value '0.000000' out of range, expected to be in range (0.000000 .. 1.000000] ptxas /tmp/tmpxft_00000776_00000000-7_polytest.compute_120.ptx, line 27; error : Unsupported modifier '.no_allocate' as secondary_priority for instruction 'createpolicy.fractional'
VARIANT 4: ptxas /tmp/tmpxft_0000078d_00000000-7_polytest.compute_120.ptx, line 27; error : Unsupported modifier '.no_allocate' as primary_priority for instruction 'createpolicy.fractional' ptxas fatal : Ptx assembly aborted due to errors
VARIANT 5: ptxas /tmp/tmpxft_000007a4_00000000-7_polytest.compute_120.ptx, line 27; error : Argument 2 of instruction 'createpolicy.fractional': value '0.000000' out of range, expected to be in range (0.000000 .. 1.000000] ptxas /tmp/tmpxft_000007a4_00000000-7_polytest.compute_120.ptx, line 27; error : Unsupported modifier '.no_allocate' as secondary_priority for instruction 'createpolicy.fractional'
Shell cwd was rese
... (43 more chars)
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`no_allocate` is rejected in fractional form entirely. Let me test the `createpolicy.range` form and then just measure what works empirically.
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stdout (287 chars)
Command running in background with ID: br0cild5r. Output is being written to: /tmp/claude-1002/-workspace-problems-03-paged-attention/008f8429-51b2-4ad0-b95e-2b6891a8d430/tasks/br0cild5r.output. You will be notified when it completes. To check interim output, use Read on that file path.
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system — task_started
↳ subagent started
tool
stdout (56 chars)
RANGE VARIANT 1: 2
RANGE VARIANT 2: 2
RANGE VARIANT 3: 2
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stdout (164 chars)
The file /workspace/problems/03_paged_attention/microbench_loads.py has been updated successfully. (file state is current in your context — no need to Read it back)
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stdout (477 chars)
32MB ldg 26.2us 1222493.9 GB/s
32MB ldcs 25.3us 1262626.3 GB/s
32MB ldcv 25.7us 1246882.8 GB/s
32MB ld_na 25.8us 1240694.7 GB/s
100MB ldg 70.8us 1412748.6 GB/s
100MB ldcs 71.1us 1406390.7 GB/s
100MB ldcv 70.7us 1415307.9 GB/s
100MB ld_na 71.2us 1403863.5 GB/s
256MB ldg 173.9us 1471941.1 GB/s
256MB ldcs 173.8us 1472754.1 GB/s
256MB ldcv 176.0us 1454281.0 GB/s
256MB ld_na 173.6us 1474926.3 GB/s
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stdout (145 chars)
File created successfully at: /workspace/problems/03_paged_attention/ab_time.py (file state is current in your context — no need to Read it back)
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stdout (471 chars)
shape=0 cold= 33.9us warm= 30.0us avg_wall_per_call= 25.3us kv=33.6MB cold_gbps= 989.2
shape=1 cold= 202.5us warm= 183.5us avg_wall_per_call= 179.0us kv=268.4MB cold_gbps= 1325.8
shape=2 cold= 70.5us warm= 60.6us avg_wall_per_call= 56.5us kv=67.1MB cold_gbps= 951.5
shape=3 cold= 84.5us warm= 70.8us avg_wall_per_call= 66.2us kv=100.6MB cold_gbps= 1190.8
shape=4 cold= 21.2us warm= 14.5us avg_wall_per_call= 9.8us kv=16.4MB cold_gbps= 774.6
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stdout (1000 chars)
==PROF== Profiling "decode_split_kernel": 0%....50%....100% - 6 passes
sm__inst_executed.avg.per_cycle_active inst/cycle 0.68
sm__inst_executed_pipe_xu.avg.pct_of_peak_sustained_active % 5.10
sm__issue_active.avg.pct_of_peak_sustained_active % 17.11
sm__pipe_alu_cycles_active.avg.pct_of_peak_sustained_active % 3.10
sm__pipe_fma_cycles_active.avg.pct_of_peak_sustained_active % 10.83
smsp__warp_issue_stalled_long_scoreboard_per_warp_active.pct % 84.82
smsp__warp_issue_stalled_math_pipe_throttle_per_warp_active.pct % 0.18
smsp__warp_issue_stalled_mio_throttle_per_warp_active.pct % 0.57
smsp__warp_issue_stalled_not_selected_per_warp_active.pct % 0.91
smsp__warp_issue_stalled_wait_per_warp_active.pct % 2.81
compaction — compact_boundary
user
This session is being continued from a previous conversation that ran out of context. The summary below covers the earlier portion of the conversation.
Summary:
1. Primary Request and Intent:
Write a high-performance paged-attention decode kernel for RTX PRO 6000 (SM120 Blackwell, GDDR7, 1.8 TB/s) in `/workspace/problems/03_paged_attention/solution.py`, keeping the same `Model`, `get_inputs`, `get_init_inputs` interface as `reference.py`. Single-query decode: query (batch, num_heads, head_dim) bf16 attends over KV cache (num_blocks, page_size=16, num_kv_heads, head_dim*2) where last dim packs [K|V]; block_table (batch, max_blocks) int32; seq_lens (batch,) int32; output bf16 (batch, num_heads, head_dim). Tolerance 0.02 abs/rel.
- Shapes to handle: (B8,H32,Hkv8,D128,L1024,P16), (B32,H32,Hkv8,D128,L2048), (B4,H64,Hkv8,D128,L4096), (B16,H32,Hkv8,D128,L1535 non-pow2), (B8,H16,Hkv4,D64,L2000 non-pow2).
- FORBIDDEN (grep-checked against solution.py text): `vllm.attention`, `flashinfer.batch_decode_with_paged_kv_cache`, `flashinfer.decode`, `torch.nn.functional.scaled_dot_product_attention`, `F.scaled_dot_product_attention` — including gather-pages-then-SDPA.
- Must be a real custom kernel (CUDA C++ load_inline / Triton / PTX / CUTLASS all allowed). Free to make scratch files in the workspace; final answer only in solution.py.
- Flywheel: implement → profile (ncu/nsys/torch.profiler) → time with benchmark.py → verify with `python check.py` (must print PASS; don't substitute one-off correctness snippets) → iterate. "Take as long as you need to actually push the number up."
- Run all Python via `uv run ...` (workspace uv environment matches scoring env). Workspace: `/workspace/problems/03_paged_attention`. Container network: bridge.
2. Key Technical Concepts:
- Flash-decoding split-K: grid (S, Hkv, B); each block does a chunk of seq with online softmax (m, l, O partials in fp32), then merge.
- GQA amortization: G = num_heads/num_kv_heads query heads share each K/V load. TG = (G*D)/32 lanes per token, E = D/TG elements per lane → configs: (D128,G4): TG16/E8/uint4; (D128,G8): TG32/E4/uint2; (D64,G4): TG8/E8/uint4.
- Scoring: peak_fraction = achieved GB/s / 1800, geomean over 5 shapes; bytes_formula = `2*B*L*Hkv*D*2 + B*H*D*2*2`. Timing: median of 30, 10 warmup, 128MB `zero_()` L2 flush + sync before each timed iter, cuda events around `fn(*inputs)` (so host enqueue counts).
- Theoretical floors: 18.7µs/149.4µs/37.3µs/56.0µs/9.1µs. Measured practical streaming ceiling under flush protocol: ~1.29 TB/s @32MB, 1.48 @100MB, 1.54 TB/s @256MB.
- Semaphore fused reduction: `atomicInc(&sem[pair], Sb-1)` auto-wraps to 0 (no reset); `__threadfence(); __syncthreads();` then last block merges partials. Sb = min(S, ceil(len/chunk)) since blocks with t0≥len early-return.
- Numeric safety: m initialized to -1e30 (not -INF) so exp2f never sees NaN ((-inf)-(-inf)); scale*log2e folded into q registers; exp2f throughout; fp32 accumulation.
- Group-masked `__shfl_xor_sync` (mask = ((1<<TG)-1) << (grp*TG)) — required because lane groups in same warp can exit loop at different trip counts.
- check.py details: 3 seeds × 3 numeric stress cases (nominal; small_q_kv inputs×1e-2 tol atol5e-4/rtol5e-2; large_q_kv inputs×8.0 tol atol5e-2/rtol5e-2); state_dict must be empty (register `_dummy` buffer with persistent=False); framework label grep (load_inline/__global__ → cuda_raw).
- ncu usage: `--cache-control all --clock-control none` for cold-cache kernel timing (clean invalidate, no dirty lines).
- PTX findings on sm_120a: `createpolicy.fractional.L2::evict_first.b64` compiles; `no_allocate` is NOT supported (neither primary nor secondary, neither fractional nor range form). Load policy (__ldg/__ldcs/__ldcv/L1::no_allocate) makes NO measurable difference for streaming reads.
- Diagnosis: kernel is memory-LATENCY bound: warm≈cold times; ncu shape1: issue_active 17.1%, long_scoreboard stalls 84.8%, 0.68 inst/cycle, 118 regs → 2×256-thread blocks/SM (16/48 warps). Wave quantization hurts shape3 (640 blocks / 376-block wave = 1.7 waves).
3. Files and Code Sections:
- `/workspace/problems/03_paged_attention/solution.py` (THE deliverable, current = v2, PASSES check.py):
- Module knobs BATCH/NUM_HEADS/... mirroring reference; `get_inputs()`/`get_init_inputs()` copied from reference.
- `_CPP_SRC`: declaration `void paged_decode(at::Tensor q, kv, bt, sl, out, o_part, ml, sem, int64_t S, int64_t chunk, int64_t nwarps, double qscale);`
- `_CUDA_SRC` kernel core (template <int D, int G, int NWARPS>, `__launch_bounds__(NWARPS*32)`):
```cpp
constexpr int TG=(G*D)/32, E=D/TG, TPW=32/TG, NS=NWARPS*TPW;
using KVec = VecT<E*2>::type; // uint2 or uint4
// grid: (split=blockIdx.x, kvh=blockIdx.y, b=blockIdx.z)
const int len=seq_lens[b]; const int Sb=min(S,(len+chunk-1)/chunk);
const int t0=split*chunk; if (t0>=len) return; const int tend=min(t0+chunk,len);
__shared__ int sm_pages[256]; __shared__ float sm_m[NWARPS][G], sm_l[NWARPS][G], sm_o[NWARPS][G][D]; __shared__ unsigned sm_last;
// cooperative page-table stage; q loaded as KVec per g, scaled by qscale
// main loop with 2-stage prefetch:
int t=t0+stream; KVec kk,vv; if (t<tend){ kp=kvc+(int64_t)sm_pages[(t-t0)>>4]*(16*slot_stride)+(t&15)*slot_stride+kvh_off; kk=__ldcs(...); vv=__ldcs(kp+D);}
for (; t<tend;){ ck=kk,cv=vv; tn=t+NS; if(tn<tend){...prefetch kk,vv...}
unpack_bf16<E>; dot fmaf chain per g; butterfly: for off=TG/2..1: s[g]+=__shfl_xor_sync(grp_mask,s[g],off);
per g: mn=fmaxf(m,s); sc=exp2f(m-mn); p=exp2f(s-mn); l=fmaf(l,sc,p); m=mn; o[e]=fmaf(o[e],sc,p*vf[e]); t=tn; }
// warp merge: for off=TG..16<<1: shfl m,l,o with wa/wb=exp2f weights
// grp==0 writes sm_o/sm_m/sm_l; __syncthreads();
// block merge over idx<G*D: M=max over warps, L,O weighted; if Sb==1 write bf16 out, else write o_part fp32 (B,Hkv,S,G,D) + ml (M,L at d==0)
if (Sb==1) return;
__threadfence(); __syncthreads();
if (threadIdx.x==0) sm_last = (atomicInc(&sem[b*Hkv+kvh],(unsigned)(Sb-1))==(unsigned)(Sb-1));
__syncthreads(); if (!sm_last) return;
// last block: merge Sb splits from o_part/ml_part, write bf16 out
```
- Host `paged_decode`: derives B,H,D,Hkv,G,maxb from tensor sizes; `dim3 grid(S,Hkv,B)`; LAUNCH macro dispatch: (128,4,{4,8,16}), (128,8,{4,8,16}), (64,4,{2,4,8}), (64,8,{4,8}).
- `_get_ext()`: `os.environ["TORCH_CUDA_ARCH_LIST"]="12.0a"`; load_inline(name="paged_decode_v2", extra_cuda_cflags=["-O3","--use_fast_math"], functions=["paged_decode"]).
- `_plan(batch, num_kv_heads, group, head_dim, seq_len)`: consults `_PLANS` dict (empty, to be filled with tuned values), else S = ceil(target/pairs) with target=env PD_TARGET_BLOCKS or 576; nwarps = env PD_NWARPS or (8 if D==128 else 4).
- `Model.__init__`: chunk = max(16, round16(ceil(L/S))) capped 4096; S recomputed = ceil(L/chunk); allocates `_out` (B,H,D bf16), `_opart` (B,Hkv,S,G,D fp32), `_ml` (B,Hkv,S,G,2 fp32), `_sem` torch.zeros(B,Hkv,int32) on cuda; `_supported` checks page_size==16 and (D,G) in {(128,4),(128,8),(64,4),(64,8)}; `self._fn = _get_ext().paged_decode`.
- `Model.forward`: single ext call `self._fn(query, kv_cache, block_table, seq_lens, self._out, self._opart, self._ml, self._sem, self.S, self.chunk, self.nwarps, self.qscale)`; returns self._out. `_fallback` pure-torch path for unsupported configs (einsum softmax, no SDPA).
- qscale = (1/sqrt(D)) * log2(e) = scale*1.4426950408889634.
- `/workspace/problems/03_paged_attention/bench_dev.py`: per-shape timing via src.eval.timing.time_fn + torch.profiler kernel breakdown. Usage: `uv run python bench_dev.py [shape_idx]`.
- `/workspace/problems/03_paged_attention/prof_one.py`: runs one shape N iters for ncu (`uv run python prof_one.py <idx> <iters>`).
- `/workspace/problems/03_paged_attention/ab_time.py`: cold (flush) vs warm (no flush) event timing + avg wall per back-to-back call.
- `/workspace/problems/03_paged_attention/microbench_loads.py`: streaming-read BW by load policy (ldg/ldcs/ldcv/L1::no_allocate) under dirty-flush protocol (NOTE: its GB/s print is off by 1024×; read the µs).
- Read-only context: reference.py, check.py, benchmark.py, shapes.py, sota.py, problem.yaml, /workspace/src/eval/{timing,correctness,numeric_stress}.py, /workspace/src/hardware/rtx_pro_6000.py (peak_bandwidth_gb_s=1800).
- /tmp/polytest.cu, /tmp/polytest2.cu (createpolicy syntax probes), /tmp/ptx_isa.pdf (downloaded, unconverted).
4. Errors and fixes:
- TORCH_CUDA_ARCH_LIST setdefault ineffective → built 6 gencodes; fixed with explicit `os.environ["TORCH_CUDA_ARCH_LIST"] = "12.0a"`.
- ptxas error "Unsupported modifier '.no_allocate' as primary_priority for createpolicy.fractional" (and as secondary, and in .range form, fraction 0.0 also out of range) → concluded L2 no_allocate unavailable on sm_120a; abandoned; empirically load policies don't matter anyway.
- v2 shape3 regression (0.715→0.639): caused by wave quantization (640 blocks, 2 blocks/SM ⇒ 1.7 waves) + fused-reduce tail; fix planned via S sweep / persistent-style balance.
- Shfl-divergence hazard (groups exiting loop at different iterations) preemptively fixed with group-local masks `grp_mask`.
- NaN hazard exp2f(-inf - -inf) fixed by NEG_INF = -1e30f init.
- microbench GB/s print bug (off by 1024) — noted, interpreted µs directly instead.
5. Problem Solving:
- v1 (two kernels): check PASS, benchmark geomean 0.5495 (fractions 0.507/0.731/0.471/0.715/0.401).
- v2 (fused semaphore + prefetch): check PASS; bench_dev fractions 0.513/0.729/0.511/0.639/0.383 (shape2 +0.04, shape3 −0.08).
- Established measurement truths: (a) torch.profiler times are L2-warm; (b) ncu --cache-control all gives clean-cold; (c) harness e2e includes ~3-8µs host enqueue inside the event window; (d) practical DRAM streaming ceiling ~1.54TB/s (85%), lower at small sizes due to ramp.
- DIAGNOSIS (latest): kernel is memory-latency bound — warm≈cold (e.g. shape4 14.5 vs 21.2µs), ncu shape1: long_scoreboard 84.82%, issue_active 17.11%, inst/cycle 0.68, fma pipe 10.8%; 118 regs limits to 2×256thr blocks/SM (16 warps = 31% occupancy); 2-stage prefetch gives only ~1KB in flight per warp.
- Improvement levers identified, in planned order: (1) sweep S (PD_TARGET_BLOCKS) and NWARPS per shape incl. wave balance (376-block waves), hardcode into _PLANS; (2) deepen the pipeline (4-stage prefetch / more tokens in flight per stream) and/or cut registers for 3 blocks/SM; (3) optionally persistent-grid scheduling for balance; (4) bigger rewrite option: tensor-core mma m16n8k16 bf16 path (FlashInfer-style GQA decode) to collapse instruction count if needed.
- ab_time.py v2 data: shape0 cold33.9/warm30.0/wall25.3; shape1 202.5/183.5/179.0; shape2 70.5/60.6/56.5; shape3 84.5/70.8/66.2; shape4 21.2/14.5/9.8 (µs).
6. All user messages:
- Initial task (paraphrased, full constraints preserved above in §1): write paged attention decode kernel for RTX PRO 6000 SM120; reference in reference.py, answer in solution.py with same interface; can make any mess in the directory but final answer in solution.py; forbidden ops list (vllm.attention, flashinfer.batch_decode_with_paged_kv_cache, flashinfer.decode, torch.nn.functional.scaled_dot_product_attention, F.scaled_dot_product_attention, including gather-then-SDPA trick); try CUDA C++ load_inline / Triton / PTX / CUTLASS; look up docs and clone reference repos as needed; flywheel = implement → profile (ncu, nsys, torch.profiler) → benchmark.py → check.py (must print PASS; don't substitute spot-checks) → iterate; push the number up; workspace is /workspace/problems/03_paged_attention (write solution.py in current dir only); run Python via `uv run`; container system python is NOT the scoring env.
- (No other user messages; remaining inputs were tool results and system reminders.)
7. Pending Tasks:
- Task #3 (in_progress): "Benchmark and iterate on bandwidth fraction" — tune splits/warps, fix latency-boundedness, reduce host overhead, re-verify check.py PASS, maximize geomean peak_fraction.
8. Current Work:
Just completed the bottleneck diagnosis for v2. The last command was ncu issue/stall metrics on shape 1's `decode_split_kernel`, returning: `sm__inst_executed 0.68 inst/cycle, issue_active 17.11%, long_scoreboard 84.82%, math_pipe_throttle 0.18%, mio_throttle 0.57%, fma pipe 10.83%, alu 3.10%, xu 5.10%`. This confirms the kernel is memory-latency bound (warps stalled waiting on loads), not instruction-issue bound — consistent with ab_time.py showing warm≈cold across shapes. Immediately before that I had stated the plan: "1. ncu issue/stall analysis (5 min) to confirm hypothesis. 2. Quick sweep S/NWARPS for all shapes (30 min) → pick best plans, update defaults. 3. Then commit to the mma rewrite (the real win), keeping scalar path as fallback" — though the ncu result (latency-bound, math pipes idle at ~11%) means deeper prefetch + occupancy improvements should come before/alongside any mma rewrite, since issue slots are not the limiter.
9. Optional Next Step:
Per the stated plan ("Quick sweep S/NWARPS for all shapes → pick best plans, update defaults"), and informed by the 84.82% long-scoreboard finding:
1) Write a sweep script that, per shape, varies PD_TARGET_BLOCKS (e.g. 188/376/564/752/1128 → S values) and PD_NWARPS (4/8/16 for D128; 2/4/8 for D64), timing with the time_fn protocol, and record the best (S, nwarps) into the `_PLANS` dict in solution.py keyed by (B, Hkv, G, D, L).
2) Increase memory-level parallelism in `decode_split_kernel` — deepen the software pipeline from 2-stage to 3/4-stage prefetch (multiple tokens in flight per stream) and/or reduce per-thread registers (118→<85, e.g. smaller block + reg tuning) to fit 3+ blocks/SM, targeting the long_scoreboard stalls.
3) Re-run `uv run python check.py` (must PASS) and `uv run python benchmark.py` after each change; keep shape3's wave balance in mind (aim for ~integer multiples of the 376-block wave or persistent scheduling).
If you need specific details from before compaction (like exact code snippets, error messages, or content you generated), read the full transcript at: /home/agent/.claude/projects/-workspace-problems-03-paged-attention/008f8429-51b2-4ad0-b95e-2b6891a8d430.jsonl
Continue the conversation from where it left off without asking the user any further questions. Resume directly — do not acknowledge the summary, do not recap what was happening, do not preface with "I'll continue" or similar. Pick up the last task as if the break never happened.
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1 """Paged-attention decode kernel for SM120 (RTX PRO 6000 Blackwell).
2
3 Flash-decoding style split-K CUDA kernel (torch.utils.cpp_extension.load_inline):
4 - One threadblock per (batch, kv_head, split). Each block streams its chunk of
5 the KV cache exactly once (K and V share a 512B segment, gathered via the
6 page table staged in shared memory), computes online softmax for the
7 G = num_heads/num_kv_heads grouped query heads with 8/16B vector loads and
8 a 2-stage register prefetch pipeline.
9 - Split partials (fp32 O, m, l) are merged by the LAST finishing block of each
10 (batch, kv_head) group — detected with an auto-resetting atomicInc semaphore
11 — so the whole decode is a single kernel launch.
12 """
13 import math
14 import os
15
16 import torch
17 import torch.nn as nn
18
19 OP_TYPE = "attention"
20 SUPPORTED_PRECISIONS = ["bf16"]
21 HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]
22
23 # --- Shape knobs (kept for interface parity with reference.py) -------------
24 BATCH = 8
25 NUM_HEADS = 32
26 NUM_KV_HEADS = 8
27 HEAD_DIM = 128
28 SEQ_LEN = 1024
29 PAGE_SIZE = 16
30
31 _CPP_SRC = r"""
32 #include <torch/extension.h>
33 void paged_decode(at::Tensor q, at::Tensor kv, at::Tensor bt, at::Tensor sl,
34 at::Tensor out, at::Tensor o_part, at::Tensor ml, at::Tensor sem,
35 int64_t S, int64_t chunk, int64_t nwarps, double qscale);
36 """
37
38 _CUDA_SRC = r"""
39 #include <torch/extension.h>
40
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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<tool_use_error>String to replace not found in file.
String: // 2-stage software pipeline: K/V for token t prefetched at t-NS.
int t = t0 + stream;
KVec kk, vv;
if (t < tend) {
const bf16* kp = kvc + (int64_t)sm_pages[(t - t0) >> 4] * (16 * slot_stride) +
(t & 15) * slot_stride + kvh_off;
kk = __ldcs(reinterpret_cast<const KVec*>(kp));
vv = __ldcs(reinterpret_cast<const KVec*>(kp + D));
}
for (; t < tend; ) {
const KVec ck = kk, cv = vv;
const int tn = t + NS;
if (tn < tend) {
const bf16* kp = kvc + (int64_t)sm_pages[(tn - t0) >> 4] * (16 * slot_stride) +
(tn - t0, tn & 15, 0) * slot_stride + kvh_off;
kk = __ldcs(reinterpret_cast<const KVec*>(kp));
vv = __ldcs(reinterpret_cast<const KVec*>(kp + D));
}
float kf[E], vf[E];
unpack_bf16<E>(&ck, kf);
unpack_bf16<E>(&cv, vf);</tool_use_error>
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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There's a variable shadowing issue — the loop index `p` vs probability `p` in the softmax update. Renaming the latter.
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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Now the partial write (normalized bf16) and the final merge.
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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Now the host dispatch with the PF dimension.
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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Now the sweep script.
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File created successfully at: /workspace/problems/03_paged_attention/sweep.py (file state is current in your context — no need to Read it back)
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/workspace/.venv/lib/python3.11/site-packages/torch/profiler/profiler.py:224: UserWarning: Warning: Profiler clears events at the end of each cycle.Only events from the current cycle will be reported.To keep events across cycles, set acc_events=True.
_warn_once(
shape=0 ms= 36.4us gbps= 925.8 frac=0.5144 S=8 chunk=128 nwarps=8
25.3us x1 void decode_split_kernel<128, 4, 8, 2>(__nv_bfloat16 const*, __nv_bfloat16 const*, int con
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Compiles and matches v2 baseline (0.514 at PF=2). Verifying correctness of the bf16-partial merge with check.py before sweeping.
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PASS. Running the full sweep now.
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--- shape 0 (B8 Hkv8 D128 L1024)
S= 2 chunk= 512 W=8 PF=2 32.9us 1022.5 GB/s frac=0.5681
S= 2 chunk= 512 W=8 PF=3 33.0us 1021.0 GB/s frac=0.5672
S= 2 chunk= 512 W=8 PF=4 33.1us 1017.6 GB/s frac=0.5653
S= 8 chunk= 128 W=4 PF=2 33.1us 1017.6 GB/s frac=0.5653
S= 3 chunk= 352 W=8 PF=3 33.5us 1005.4 GB/s frac=0.5586
S= 8 chunk= 128 W=4 PF=4 33.5us 1004.9 GB/s frac=0.5583
S= 4 chunk= 256 W=4 PF=2 33.6us 1004.0 GB/s frac=0.5578
S= 8 chunk= 128 W=4 PF=3 33.6us 1004.0 GB/s frac=0.5578
--- shape 1 (B32 Hkv8 D128 L2048)
S= 1 chunk= 2048 W=8 PF=2 182.8us 1471.6 GB/s frac=0.8176
S= 1 chunk= 2048 W=4 PF=4 183.2us 1468.4 GB/s frac=0.8158
S= 1 chunk= 2048 W=8 PF=3 183.4us 1466.2 GB/s frac=0.8146
S= 2 chunk= 1024 W=4 PF=2 183.9us 1462.4 GB/s frac=0.8124
S= 1 chunk= 2048 W=8 PF=4 184.0us 1462.1 GB/s frac=0.8123
S= 2 chunk= 1024 W=4 PF=4 184.1us 1460.6 GB/s frac=0.8114
S= 1 chunk= 2048 W=4 PF=2 184.7us 1455.9 GB/s frac=0.8088
S= 2 chunk= 1024 W=4 PF=3 185.2us 1452.5 GB/s frac=0.8070
--- shape 2 (B4 Hkv8 D128 L4096)
S= 9 chunk= 464 W=8 PF=2 58.8us 1143.2 GB/s frac=0.6351
S= 9 chunk= 464 W=8 PF=3 60.4us 1112.4 GB/s frac=0.6180
S= 9 chunk= 464 W=8 PF=4 60.6us 1109.7 GB/s frac=0.6165
S= 18 chunk= 240 W=4 PF=2 63.9us 1051.7 GB/s frac=0.5843
S= 18 chunk= 240 W=4 PF=3 64.6us 1041.3 GB/s fr
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The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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The file /workspace/problems/03_paged_attention/sweep.py has been updated successfully. (file state is current in your context — no need to Read it back)
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stdout (287 chars)
Command running in background with ID: bddji8kvv. Output is being written to: /tmp/claude-1002/-workspace-problems-03-paged-attention/008f8429-51b2-4ad0-b95e-2b6891a8d430/tasks/bddji8kvv.output. You will be notified when it completes. To check interim output, use Read on that file path.
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system — task_started
↳ subagent started
tool
stdout (103 chars)
/kbh/bin/ncu
NVIDIA (R) Nsight Compute Command Line Profiler
Copyright (c) 2018-2025 NVIDIA Corporation
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stdout (2862 chars) — TRUNCATED
--- shape 0 (B8 Hkv8 D128 L1024)
S= 2 chunk= 512 W=16 PF=2 33.2us 1013.6 GB/s frac=0.5631
S= 2 chunk= 512 W=8 PF=3 33.4us 1008.8 GB/s frac=0.5604
S= 2 chunk= 512 W=8 PF=2 33.5us 1004.5 GB/s frac=0.5580
S= 2 chunk= 512 W=16 PF=3 33.8us 996.4 GB/s frac=0.5535
S= 4 chunk= 256 W=8 PF=3 33.8us 995.4 GB/s frac=0.5530
S= 4 chunk= 256 W=8 PF=2 34.0us 990.8 GB/s frac=0.5504
S= 2 chunk= 512 W=8 PF=4 34.0us 989.8 GB/s frac=0.5499
S= 3 chunk= 352 W=8 PF=3 34.4us 980.6 GB/s frac=0.5448
--- shape 1 (B32 Hkv8 D128 L2048)
S= 1 chunk= 2048 W=16 PF=2 182.9us 1470.6 GB/s frac=0.8170
S= 1 chunk= 2048 W=8 PF=2 183.2us 1468.1 GB/s frac=0.8156
S= 1 chunk= 2048 W=8 PF=4 184.3us 1459.5 GB/s frac=0.8108
S= 2 chunk= 1024 W=8 PF=2 188.5us 1426.6 GB/s frac=0.7926
S= 2 chunk= 1024 W=16 PF=2 189.7us 1417.7 GB/s frac=0.7876
S= 2 chunk= 1024 W=8 PF=4 194.3us 1384.3 GB/s frac=0.7691
S= 1 chunk= 2048 W=16 PF=4 199.9us 1345.8 GB/s frac=0.7476
S= 2 chunk= 1024 W=16 PF=4 200.8us 1339.1 GB/s frac=0.7440
--- shape 2 (B4 Hkv8 D128 L4096)
S= 9 chunk= 464 W=8 PF=2 60.1us 1118.0 GB/s frac=0.6211
S= 9 chunk= 464 W=8 PF=3 60.4us 1112.7 GB/s frac=0.6181
S= 9 chunk= 464 W=8 PF=4 60.4us 1112.4 GB/s frac=0.6180
S= 9 chunk= 464 W=16 PF=2 63.0us 1068.0 GB/s frac=0.5933
S= 9 chunk= 464 W=16 PF=3 64.7us 1039.4
... (1362 more chars)
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subagent · 0 events · 0 tools
tool
stderr (98 chars)
Exit code 1
=== shape 0 S=2 W=8 PF=2 ===
=== shape 2 S=9 W=8 PF=2 ===
=== shape 4 S=4 W=8 PF=6 ===
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tool
stdout (102 chars)
malloc(): mismatching next->prev_size (unsorted)
==ERROR== The application returned an error code (6).
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tool
stdout (1444 chars)
==WARNING== Note: Running with unmodified GPU clocks. If not controlled otherwise, profiling results may be inconsistent.
==PROF== Connected to process 3413 (/uv-cache/python/cpython-3.11.15-linux-x86_64-gnu/bin/python3.11)
==PROF== Profiling "decode_split_kernel": 0%....50%....100% - 1 pass
==PROF== Disconnected from process 3413
[3413] python3.11@127.0.0.1
void decode_split_kernel<128, 4, 8, 2>(const __nv_bfloat16 *, const __nv_bfloat16 *, const int *, const int *, __nv_bfloat16 *, float *, unsigned int *, __nv_bfloat16 *, int, int, int, int, float) (2, 8, 8)x(256, 1, 1), Context 1, Stream 7, Device 0, CC 12.0
Warning: Data collection happened without fixed GPU frequencies. Profiling results may be inconsistent.
Section: Command line profiler metrics
------------------------------------------------------ ----------- ------------
Metric Name Metric Unit Metric Value
------------------------------------------------------ ----------- ------------
dram__bytes_read.sum (!) n/a
dram__bytes_write.sum (!) n/a
gpu__dram_throughput.avg.pct_of_peak_sustained_elapsed % 74.64
gpu__time_duration.sum us 26.43
------------------------------------------------------ ----------- ------------
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tool
stdout (331 chars)
gpu__dram_throughput.avg.pct_of_peak_sustained_elapsed % 75.27
gpu__time_duration.sum us 52.29
gpu__dram_throughput.avg.pct_of_peak_sustained_elapsed % 60.99
gpu__time_duration.sum us 15.84
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tool
stdout (156 chars)
The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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subagent · 0 events · 0 tools
tool
stdout (143 chars)
shape=0 ms= 32.4us gbps= 1039.2 frac=0.5773 S=2 chunk=512 nwarps=8
shape=4 ms= 20.8us gbps= 788.1 frac=0.4378 S=4 chunk=512 nwarps=8
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subagent · 0 events · 0 tools
tool
stdout (1025 chars)
shape=1 solution_peak_fraction=0.7491
benchmark_event event=variant_start shape=2 variant=solution ts=2026-06-11T12:00:49.654681+00:00
benchmark_event event=variant_end shape=2 variant=solution ts=2026-06-11T12:00:49.659805+00:00 elapsed_s=0.005 ms=0.068464
shape=2 variant=solution tflops=7.842 gbps=982.121 ms=0.068
shape=2 solution_peak_fraction=0.5456
benchmark_event event=variant_start shape=3 variant=solution ts=2026-06-11T12:00:50.263953+00:00
benchmark_event event=variant_end shape=3 variant=solution ts=2026-06-11T12:00:50.269920+00:00 elapsed_s=0.006 ms=0.085088
shape=3 variant=solution tflops=4.729 gbps=1185.360 ms=0.085
shape=3 solution_peak_fraction=0.6585
benchmark_event event=variant_start shape=4 variant=solution ts=2026-06-11T12:00:50.368281+00:00
benchmark_event event=variant_end shape=4 variant=solution ts=2026-06-11T12:00:50.371713+00:00 elapsed_s=0.003 ms=0.022224
shape=4 variant=solution tflops=2.949 gbps=738.695 ms=0.022
shape=4 solution_peak_fraction=0.4104
peak_fraction: 0.5643
RESULT: OK
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Benchmark with untuned defaults: 0.5643. Filling `_PLANS` with the sweep winners.
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tool
stdout (156 chars)
The file /workspace/problems/03_paged_attention/solution.py has been updated successfully. (file state is current in your context — no need to Read it back)
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subagent · 0 events · 0 tools
tool
stdout (222 chars)
shape=0 solution_peak_fraction=0.5745
shape=1 solution_peak_fraction=0.8205
shape=2 solution_peak_fraction=0.6331
shape=3 solution_peak_fraction=0.7395
shape=4 solution_peak_fraction=0.4385
peak_fraction: 0.6268
RESULT: OK