./kernelbenchhardv3runsopencode · ?
opencode / ? session: ses_230929a38ffehjfs8CqZ1tnEyM cwd: ?
harness
opencode
model
?
turns
61
tools called
33
events
91
input toks
65,358
output toks
13,136
cache hit
1,116,544
solution.py
final answer
benchmark.log
check.log
result.json
"""Paged attention decode kernel for RTX PRO 6000 (SM120 Blackwell).

Single-query decode with grouped-query attention (GQA).
One 32-thread warp-block per query head for maximum parallelism.
Each lane handles D/32 dimensions; all reduction via __shfl_xor_sync.
Online softmax processes KV cache in a single streaming pass.
"""
from __future__ import annotations

import math

import torch
import torch.nn as nn
from torch.utils.cpp_extension import load_inline

OP_TYPE = "attention"
SUPPORTED_PRECISIONS = ["bf16"]
HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]

BATCH = 8
NUM_HEADS = 32
NUM_KV_HEADS = 8
HEAD_DIM = 128
SEQ_LEN = 1024
PAGE_SIZE = 16

# ---------------------------------------------------------------------------
# CUDA kernel + wrapper
# ---------------------------------------------------------------------------

_cpp_src = r"""
torch::Tensor launch_paged_attention_decode(
    torch::Tensor query,
    torch::Tensor kv_cache,
    torch::Tensor block_table,
    torch::Tensor seq_lens,
    int B, int H, int Hkv, int D, int P, int max_blocks, float scale);
"""

_cuda_src = r"""
#include <cuda_runtime.h>
#include <cuda_fp16.h>
#include <cuda_bf16.h>

#define WARP_SIZE 32
#define MAX_STRIDE 8

extern "C" __global__ void paged_attention_decode_kernel(
    const __nv_bfloat16* __restrict__ query,
    const __nv_bfloat16* __restrict__ kv_cache,
    const int* __restrict__ block_table,
    const int* __restrict__ seq_lens,
    __nv_bfloat16* __restrict__ output,
    int B, int H, int Hkv, int D, int P, int max_blocks, float scale,
    int G)
{
    // One block per query head
    int linear_bid = blockIdx.x;
    int b      = linear_bid / H;
    int q_head = linear_bid % H;
    if (b >= B) return;

    int L = seq_lens[b];
    if (L <= 0) return;

    int kv_h = q_head / G;   // which KV head this query head maps to
    int num_pages = (L + P - 1) / P;
    int lane_id = threadIdx.x;
    int stride  = D / WARP_SIZE;
    unsigned mask = __activemask();

    // Load this query head (fp32)
    float q_val[MAX_STRIDE];
    int q_base = b * H * D + q_head * D;
    #pragma unroll
    for (int s = 0; s < stride; s++) {
        q_val[s] = __bfloat162float(query[q_base + lane_id + s * WARP_SIZE]);
    }

    // Online softmax state for this single query head
    float m = -1e10f;
    float l = 0.0f;
    float acc[MAX_STRIDE];
    #pragma unroll
    for (int s = 0; s < stride; s++) {
        acc[s] = 0.0f;
    }

    // Offsets into kv_cache for this KV head
    const int* bt_base = block_table + b * max_blocks;
    int page_stride  = P * Hkv * 2 * D;
    int token_stride = Hkv * 2 * D;
    int k_off = kv_h * 2 * D;
    int v_off = k_off + D;

    // Main loop over pages and tokens
    for (int pg = 0; pg < num_pages; pg++) {
        int block_idx = bt_base[pg];
        int page_base = block_idx * page_stride;
        int tokens = (pg == num_pages - 1) ? (L - pg * P) : P;

        for (int t = 0; t < tokens; t++) {
            int base = page_base + t * token_stride;

            // Load K and V values for this token (strided across lanes)
            float k_vals[MAX_STRIDE];
            float v_vals[MAX_STRIDE];
            #pragma unroll
            for (int s = 0; s < stride; s++) {
                int idx = lane_id + s * WARP_SIZE;
                k_vals[s] = __bfloat162float(kv_cache[base + k_off + idx]);
                v_vals[s] = __bfloat162float(kv_cache[base + v_off + idx]);
            }

            // Dot product: Q @ K
            float dot = 0.0f;
            #pragma unroll
            for (int s = 0; s < stride; s++) {
                dot += q_val[s] * k_vals[s];
            }
            // Warp-level butterfly reduction
            #pragma unroll
            for (int offset = WARP_SIZE / 2; offset > 0; offset >>= 1) {
                dot += __shfl_xor_sync(mask, dot, offset);
            }
            dot *= scale;

            // Online softmax — lane 0 computes, then broadcast
            float weight_val = 0.0f;
            float rescale_val = 0.0f;
            if (lane_id == 0) {
                float m_new = fmaxf(m, dot);
                float old_scale = __expf(m - m_new);
                float exp_val   = __expf(dot - m_new);
                weight_val  = exp_val;
                rescale_val = old_scale;
                l = old_scale * l + exp_val;
                m = m_new;
            }
            weight_val  = __shfl_sync(mask, weight_val,  0);
            rescale_val = __shfl_sync(mask, rescale_val, 0);

            // Update output accumulator
            #pragma unroll
            for (int s = 0; s < stride; s++) {
                acc[s] = rescale_val * acc[s] + weight_val * v_vals[s];
            }
        }
    }

    // Normalise and write output
    float l_final = __shfl_sync(mask, l, 0);
    int out_base = b * H * D + q_head * D;
    #pragma unroll
    for (int s = 0; s < stride; s++) {
        output[out_base + lane_id + s * WARP_SIZE] = __float2bfloat16(acc[s] / l_final);
    }
}

// -----------------------------------------------------------------------
// C++ wrapper
// -----------------------------------------------------------------------
torch::Tensor launch_paged_attention_decode(
    torch::Tensor query,
    torch::Tensor kv_cache,
    torch::Tensor block_table,
    torch::Tensor seq_lens,
    int B, int H, int Hkv, int D, int P, int max_blocks, float scale)
{
    auto output = torch::empty({B, H, D}, query.options());

    constexpr int THREADS = 32;
    int G = H / Hkv;
    int num_blocks = B * H;

    paged_attention_decode_kernel<<<num_blocks, THREADS>>>(
        reinterpret_cast<const __nv_bfloat16*>(query.data_ptr<torch::BFloat16>()),
        reinterpret_cast<const __nv_bfloat16*>(kv_cache.data_ptr<torch::BFloat16>()),
        block_table.data_ptr<int>(),
        seq_lens.data_ptr<int>(),
        reinterpret_cast<__nv_bfloat16*>(output.data_ptr<torch::BFloat16>()),
        B, H, Hkv, D, P, max_blocks, scale, G);

    return output;
}
"""

_module = None

def _get_module():
    global _module
    if _module is None:
        _module = load_inline(
            name="paged_attention_decode_ext",
            cpp_sources=[_cpp_src],
            cuda_sources=[_cuda_src],
            functions=["launch_paged_attention_decode"],
            extra_cuda_cflags=[
                "-std=c++17",
                "-O3",
                "--use_fast_math",
                "-gencode", "arch=compute_120,code=sm_120",
            ],
            extra_cflags=["-O3"],
            verbose=False,
        )
    return _module


# ---------------------------------------------------------------------------
# Model
# ---------------------------------------------------------------------------

class Model(nn.Module):
    """Single-query paged attention decode -- custom CUDA kernel."""

    def __init__(
        self,
        batch: int,
        num_heads: int,
        num_kv_heads: int,
        head_dim: int,
        seq_len: int,
        page_size: int,
    ):
        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.scale = 1.0 / math.sqrt(head_dim)
        self.register_buffer("_dummy", torch.zeros(1, dtype=torch.bfloat16), persistent=False)

    def forward(
        self,
        query: torch.Tensor,
        kv_cache: torch.Tensor,
        block_table: torch.Tensor,
        seq_lens: torch.Tensor,
    ) -> torch.Tensor:
        B, H, D = query.shape
        max_blocks = block_table.shape[1]

        mod = _get_module()
        return mod.launch_paged_attention_decode(
            query.contiguous(),
            kv_cache.contiguous(),
            block_table.contiguous(),
            seq_lens.contiguous(),
            B, H, self.num_kv_heads, D, self.page_size, max_blocks, self.scale,
        )


# ---------------------------------------------------------------------------
# Input factories
# ---------------------------------------------------------------------------

def get_inputs():
    B = BATCH
    H = NUM_HEADS
    Hkv = NUM_KV_HEADS
    D = HEAD_DIM
    L = SEQ_LEN
    P = 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]
The warp-only kernel didn't help. The problem is occupancy — with B*Hkv blocks and only 1 warp each, we have too few blocks for small batch sizes. Let me switch to B*H blocks (one per query head) which gives G× more parallelism. The KV cache will be re-read G times but this matches what the reference does after `repeat_interleave`.
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] Graph break from `Tensor.item()`, consider setting:
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     torch._dynamo.config.capture_scalar_outputs = True
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] or:
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     env TORCHDYNAMO_CAPTURE_SCALAR_OUTPUTS=1
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] to include these operations in the captured graph.
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] Graph break: from user code at:
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]   File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/reference.py", line 89, in forward
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     L = int(seq_lens[b].item())
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 
W0427 09:25:00.605000 1131347 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 
  [sota unavailable] ValueError: The dtype of q torch.bfloat16 does not match the q_data_type torch.float16 specified in plan function.
shape=0 variant=eager tflops=0.230 gbps=57.830 ms=0.582
shape=0 variant=compiled tflops=0.225 gbps=56.407 ms=0.597
shape=0 variant=solution tflops=0.191 gbps=47.896 ms=0.703
shape=0 solution_peak_fraction=0.0266
  [sota unavailable] ValueError: The dtype of q torch.bfloat16 does not match the q_data_type torch.float16 specified in plan function.
shape=1 variant=eager tflops=0.348 gbps=87.279 ms=3.082
shape=1 variant=compiled tflops=0.347 gbps=86.902 ms=3.095
shape=1 variant=solution tflops=0.768 gbps=192.396 ms=1.398
shape=1 solution_peak_fraction=0.1069
  [sota unavailable] ValueError: The dtype of q torch.bfloat16 does not match the q_data_type torch.float16 specified in plan function.
shape=2 variant=eager tflops=0.243 gbps=30.494 ms=2.205
shape=2 variant=compiled tflops=0.243 gbps=30.403 ms=2.212
shape=2 variant=solution tflops=0.195 gbps=24.409 ms=2.755
shape=2 solution_peak_fraction=0.0136
  [sota unavailable] ValueError: The dtype of q torch.bfloat16 does not match the q_data_type torch.float16 specified in plan function.
shape=3 variant=eager tflops=0.303 gbps=75.901 ms=1.329
shape=3 variant=compiled tflops=0.301 gbps=75.331 ms=1.339
shape=3 variant=solution tflops=0.381 gbps=95.498 ms=1.056
shape=3 solution_peak_fraction=0.0531
  [sota unavailable] ValueError: The dtype of q torch.bfloat16 does not match the q_data_type torch.float16 specified in plan function.
shape=4 variant=eager tflops=0.113 gbps=28.235 ms=0.581
shape=4 variant=compiled tflops=0.111 gbps=27.705 ms=0.593
shape=4 variant=solution tflops=0.049 gbps=12.180 ms=1.348
shape=4 solution_peak_fraction=0.0068
peak_fraction: 0.0268
RESULT: LOW
PASS
{
    "problem": "03_paged_attention",
    "harness": "opencode",
    "model": "deepseek/deepseek-v4-pro",
    "reasoning_effort": "",
    "has_solution": true,
    "correct": true,
    "peak_fraction": 0.0268,
    "elapsed_seconds": 1933,
    "harness_exit_code": 0,
    "session_complete": true,
    "usage": {"input_tokens": 65358, "output_tokens": 13136, "cache_read_tokens": 1116544, "cache_creation_tokens": 0, "reasoning_tokens": 45848, "total_cost_usd": null}
}

timeline (91 events)

assistant
read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention"
}
tool
stdout (212 chars)
<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention</path>
<type>directory</type>
<entries>
benchmark.py
check.py
problem.yaml
PROMPT.txt
reference.py
shapes.py
sota.py

(7 entries)
</entries>
assistant
read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/reference.py
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{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/reference.py"
}
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<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/reference.py</path>
<type>file</type>
<content>
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
3

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read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/check.py
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{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/check.py"
}
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<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/check.py</path>
<type>file</type>
<content>
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: 
18: 
19: def _apply_shape(reference, shape: dict) -> None:
20:     reference.BATCH = shape["batch"]
21:     reference.NUM_HEADS = shape["num_heads"]
22:     reference.NUM_KV_HEADS = shape["num_kv_heads"]
23:     reference.HEAD_DIM = shape["head_dim"]
24:     reference.SEQ_LEN = shape["seq_len"]
25:     reference.PAGE_SIZE = shape["page_size"]
26: 
27: 
28: def main():
29:     try:
30:         import reference
31:         import shapes
32:         import solution
33:     except Exception as e:
34:         print(f"FAIL: import error: {e}")
35:         sys.exit(1)
36: 
37:     problem_yaml = Path("problem.yaml")
38:     meta = yaml.safe_load(problem_yaml.read_text()) if problem_yaml.exists() else {}
39: 
40:     sol_src = Path("solution.py").read_text() if Path("solution.py").exists() else ""
41:     for forbidden in meta.get("forbidden", []):
42:         pat = re.escape(forbidden)
43:     

... (2537 more chars)
assistant
read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/benchmark.py
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{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/benchmark.py"
}
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<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/benchmark.py</path>
<type>file</type>
<content>
1: """Roofline benchmark for paged-attention decode.
2: 
3: For each shape: times eager reference, compiled reference, SOTA (if available),
4: and the agent's solution. 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 time_fn  # 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.y

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read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
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{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py"
}
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read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/shapes.py
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{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/shapes.py"
}
tool
stdout (1155 chars)
<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/shapes.py</path>
<type>file</type>
<content>
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: ]

(End of file - total 18 lines)
</content>
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read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/problem.yaml
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{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/problem.yaml"
}
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<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/problem.yaml</path>
<type>file</type>
<content>
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. SD

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assistant
read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/sota.py
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/sota.py"
}
tool
stdout (3303 chars) — TRUNCATED
<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/sota.py</path>
<type>file</type>
<content>
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].contig

... (1803 more chars)
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read /home/infatoshi/cuda/KernelBench-Hard/src/eval/correctness.py
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/src/eval/correctness.py"
}
tool
stdout (4080 chars) — TRUNCATED
<path>/home/infatoshi/cuda/KernelBench-Hard/src/eval/correctness.py</path>
<type>file</type>
<content>
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
4

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read /home/infatoshi/cuda/KernelBench-Hard/src/hardware.py
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/src/hardware.py"
}
assistant
read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/PROMPT.txt
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/PROMPT.txt"
}
tool
stdout (2753 chars) — TRUNCATED
<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/PROMPT.txt</path>
<type>file</type>
<content>
1: I need you to write a paged attention decode kernel for the RTX PRO 6000 (SM120 Blackwell, GDDR7, 1.8 TB/s). The reference implementation is in reference.py and your kernel goes in solution.py. You can make whatever mess you want in this directory — scratch files, intermediate kernels, build artifacts, profiling traces — but the final answer has to be in solution.py with the same Model, get_inputs, and get_init_inputs interface as reference.py.
2: 
3: This is single-query decode: each batch element has a query of shape (num_heads, head_dim) and attends over a KV cache of seq_len[b] tokens stored as fixed-size pages in a global pool, with block_table[b] listing which pages belong to batch element b. The KV cache is laid out as (num_blocks, page_size, num_kv_heads, head_dim * 2) where the last dim packs [K | V] so a single gather pulls both. You return the bf16 output of shape (batch, num_heads, head_dim). Correctness tolerance is 0.02 abs/rel on bf16/fp16. The shapes you have to handle are batch=8 num_heads=32 num_kv_heads=8 head_dim=128 seq_len=1024 page_size=16 (Llama-3 8B-style decode), batch=32 num_heads=32 num_kv_heads=8 head_dim=128 seq_len=2048 page_size=16 (server-batched decode), batch=4 num_heads=64 num_kv_heads=8 head_dim=128 seq_len=4096 page_size=16 (Llama-3 70B GQA wide ratio with long context), batch=16 num_heads=32 num_kv_heads=8 head_dim=128

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read /home/infatoshi/cuda/KernelBench-Hard/src/hardware
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/src/hardware"
}
tool
stdout (171 chars)
<path>/home/infatoshi/cuda/KernelBench-Hard/src/hardware</path>
<type>directory</type>
<entries>
__init__.py
__pycache__/
m4_max.py
rtx_pro_6000.py

(4 entries)
</entries>
assistant
bash
args
{
  "command": "nvidia-smi --query-gpu=name,compute_cap,memory.total --format=csv,noheader 2>&1 | head -5",
  "description": "Check GPU info"
}
tool
stdout (67 chars)
NVIDIA RTX PRO 6000 Blackwell Workstation Edition, 12.0, 97887 MiB
assistant
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read /home/infatoshi/cuda/KernelBench-Hard/src/hardware/rtx_pro_6000.py
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/src/hardware/rtx_pro_6000.py"
}
tool
stdout (1170 chars)
<path>/home/infatoshi/cuda/KernelBench-Hard/src/hardware/rtx_pro_6000.py</path>
<type>file</type>
<content>
1: """RTX PRO 6000 Blackwell Workstation — SM120, consumer-lineage Blackwell.
2: 
3: Peak tensor-core throughputs are dense-matrix advertised peaks. Actual kernels
4: will see 60-85% of peak on well-tuned code.
5: """
6: from dataclasses import dataclass
7: 
8: 
9: @dataclass(frozen=True)
10: class HardwareTarget:
11:     name: str
12:     sm: str
13:     vram_gb: int
14:     peak_bandwidth_gb_s: float  # DRAM
15:     peak_tflops_dense: dict[str, float]  # dtype -> TFLOPS
16: 
17: 
18: RTX_PRO_6000 = HardwareTarget(
19:     name="RTX PRO 6000 Blackwell Workstation",
20:     sm="sm_120a",
21:     vram_gb=96,
22:     peak_bandwidth_gb_s=1800.0,
23:     peak_tflops_dense={
24:         "fp4": 800.0,
25:         "nvfp4": 800.0,
26:         "mxfp4": 800.0,
27:         "fp6": 800.0,
28:         "fp8": 400.0,
29:         "bf16": 200.0,
30:         "fp16": 200.0,
31:         "tf32": 100.0,
32:         "fp32": 12.0,  # non-tensor-core SIMT fp32
33:         "int8": 400.0,
34:         "int4": 800.0,
35:     },
36: )

(End of file - total 36 lines)
</content>
assistant
read /home/infatoshi/cuda/KernelBench-Hard/src/hardware/__init__.py
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/src/hardware/__init__.py"
}
tool
stdout (558 chars)
<path>/home/infatoshi/cuda/KernelBench-Hard/src/hardware/__init__.py</path>
<type>file</type>
<content>
1: """Hardware peak-throughput lookup tables."""
2: from src.hardware.m4_max import M4_MAX
3: from src.hardware.rtx_pro_6000 import RTX_PRO_6000
4: 
5: TARGETS = {
6:     "RTX_PRO_6000": RTX_PRO_6000,
7:     "M4_MAX": M4_MAX,
8: }
9: 
10: 
11: def get(name: str):
12:     if name not in TARGETS:
13:         raise ValueError(f"Unknown hardware {name!r}; available: {list(TARGETS)}")
14:     return TARGETS[name]

(End of file - total 14 lines)
</content>
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bash
args
{
  "description": "Check torch load_inline API",
  "command": "python3 -c \"import torch.utils.cpp_extension; help(torch.utils.cpp_extension.load_inline)\" 2>&1 | head -80"
}
tool
stdout (4823 chars) — TRUNCATED
Help on function load_inline in module torch.utils.cpp_extension:

load_inline(name, cpp_sources, cuda_sources=None, sycl_sources=None, functions=None, extra_cflags=None, extra_cuda_cflags=None, extra_sycl_cflags=None, extra_ldflags=None, extra_include_paths=None, build_directory=None, verbose=False, with_cuda=None, with_sycl=None, is_python_module=True, with_pytorch_error_handling=True, keep_intermediates=True, use_pch=False, no_implicit_headers=False)
    Load a PyTorch C++ extension just-in-time (JIT) from string sources.

    This function behaves exactly like :func:`load`, but takes its sources as
    strings rather than filenames. These strings are stored to files in the
    build directory, after which the behavior of :func:`load_inline` is
    identical to :func:`load`.

    See `the
    tests <https://github.com/pytorch/pytorch/blob/master/test/test_cpp_extensions_jit.py>`_
    for good examples of using this function.

    Sources may omit two required parts of a typical non-inline C++ extension:
    the necessary header includes, as well as the (pybind11) binding code. More
    precisely, strings passed to ``cpp_sources`` are first concatenated into a
    single ``.cpp`` file. This file is then prepended with ``#include
    <torch/extension.h>``

    Furthermore, if the ``functions`` argument is supplied, bindings will be
    automatically generated for each function specified. ``functions`` can
    either be a list of function names, or a dictionary mapping from f

... (3323 more chars)
assistant
task
args
{
  "description": "Search load_inline usage patterns",
  "prompt": "Search the directory /home/infatoshi/cuda/KernelBench-Hard for any files that use `load_inline` or `cpp_extension.load_inline` to understand the calling convention - specifically how grid, block, and shared_mem are passed. Also look for how the kernel functions returned by load_inline are called. Return any relevant code snippets.",
  "subagent_type": "explore"
}
tool
stdout (8425 chars) — TRUNCATED
task_id: ses_23088b86cffeX6aN6lxvfBg8m2 (for resuming to continue this task if needed)

<task_result>
Now I have a complete picture. Let me provide a comprehensive answer with all findings.

---

## Results: `load_inline` / `cpp_extension.load_inline` Calling Convention in KernelBench-Hard

### Key Finding: No Existing Usage in the Repo

There are **zero actual calls to `load_inline`** anywhere in the KernelBench-Hard repository. The only references are:

1. **PROMPT.txt files** (7 of them) -- suggesting agents use `load_inline` as one possible approach:
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/01_fp8_gemm/PROMPT.txt` (line 5)
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/02_kda_cutlass/PROMPT.txt` (line 5)
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/PROMPT.txt` (line 5)
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/04_kahan_softmax/PROMPT.txt` (line 5)
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/05_topk_bitonic/PROMPT.txt` (line 5)
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/06_sonic_moe_swiglu/PROMPT.txt` (line 5)
   - `/home/infatoshi/cuda/KernelBench-Hard/problems/07_w4a16_gemm/PROMPT.txt` (line 5)

2. **check.py files** (7 of them) -- using it only as a regex detection pattern to label the framework:
   ```python
   ("cuda_raw",  r"torch\.utils\.cpp_extension\.load_inline|__global__\s+void")
   ```
   All 7 check.py files share this identical pattern (the file paths are listed above, all under `/home

... (6925 more chars)
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in 657out 237cache_r 43392cache_w 0
assistant
todowrite
args
{
  "todos": [
    {
      "content": "Write initial solution.py with CUDA C++ kernel + C++ wrapper via load_inline",
      "status": "in_progress",
      "priority": "high"
    },
    {
      "content": "Run check.py for correctness verification",
      "status": "pending",
      "priority": "high"
    },
    {
      "content": "Run benchmark.py for performance measurement",
      "status": "pending",
      "priority": "high"
    },
    {
      "content": "Profile with ncu and iterate if performance is below target",
      "status": "pending",
      "priority": "medium"
    }
  ]
}
tool
stdout (413 chars)
content: 'Write initial solution.py with CUDA C++ kernel + C++ wrapper via load_inline'
status: 'in_progress'
priority: 'high'
content: 'Run check.py for correctness verification'
status: 'pending'
priority: 'high'
content: 'Run benchmark.py for performance measurement'
status: 'pending'
priority: 'high'
content: 'Profile with ncu and iterate if performance is below target'
status: 'pending'
priority: 'medium'
assistant
Now I have a clear picture of the API. I need to put the wrapper in `cpp_sources` (with forward-declared signature) and the kernel + wrapper body in `cuda_sources`. Let me write the solution.
assistant
in 3638out 206cache_r 50944cache_w 0
assistant
bash
args
{
  "command": "ls -la /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/",
  "description": "Check current directory contents"
}
tool
stdout (559 chars)
total 44
drwxrwxr-x  2 infatoshi infatoshi 4096 Apr 27 08:52 .
drwxrwxr-x 10 infatoshi infatoshi 4096 Apr 24 00:30 ..
-rw-rw-r--  1 infatoshi infatoshi 4353 Apr 26 03:11 benchmark.py
-rw-rw-r--  1 infatoshi infatoshi 3441 Apr 25 22:20 check.py
-rw-rw-r--  1 infatoshi infatoshi 2030 Apr 25 22:19 problem.yaml
-rw-rw-r--  1 infatoshi infatoshi 2585 Apr 27 03:21 PROMPT.txt
-rw-rw-r--  1 infatoshi infatoshi 5151 Apr 25 22:19 reference.py
-rw-rw-r--  1 infatoshi infatoshi  933 Apr 25 22:19 shapes.py
-rw-rw-r--  1 infatoshi infatoshi 2819 Apr 25 22:24 sota.py
assistant
bash
args
{
  "command": "<440 chars \u2014 see below>",
  "description": "Verify CUDA environment"
}
command (440 chars)
python3 -c "
import torch
# Verify bf16 support and compute capability
print('CUDA available:', torch.cuda.is_available())
print('Device:', torch.cuda.get_device_name(0))
print('Compute cap:', torch.cuda.get_device_capability(0))
print('bf16 supported:', torch.cuda.is_bf16_supported())
# Check nvcc
import subprocess
r = subprocess.run(['nvcc', '--version'], capture_output=True, text=True)
print('nvcc version:', r.stdout.strip()[:200])
"
tool
stdout (336 chars)
CUDA available: True
Device: NVIDIA RTX PRO 6000 Blackwell Workstation Edition
Compute cap: (12, 0)
bf16 supported: True
nvcc version: nvcc: NVIDIA (R) Cuda compiler driver
Copyright (c) 2005-2026 NVIDIA Corporation
Built on Mon_Mar_02_09:52:23_PM_PST_2026
Cuda compilation tools, release 13.2, V13.2.51
Build cuda_13.2.r13.2/compiler.
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write /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
diff (323 lines — TRUNCATED)
--- /dev/null
+++ b//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
@@ -0,0 +1,320 @@
+"""Paged attention decode kernel for RTX PRO 6000 (SM120 Blackwell).
+
+Single-query decode with grouped-query attention (GQA).
+Uses online softmax to process KV cache in a single pass without gathering pages.
+One block per (batch, kv_head) pair; each thread handles one head_dim element.
+"""
+from __future__ import annotations
+
+import math
+
+import torch
+import torch.nn as nn
+from torch.utils.cpp_extension import load_inline
+
+OP_TYPE = "attention"
+SUPPORTED_PRECISIONS = ["bf16"]
+HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]
+
+# Language-visible shape knobs (overridden by check.py/benchmark.py)
+BATCH = 8
+NUM_HEADS = 32
+NUM_KV_HEADS = 8
+HEAD_DIM = 128
+SEQ_LEN = 1024
+PAGE_SIZE = 16
+
+# ---------------------------------------------------------------------------
+# CUDA kernel + wrapper (compiled once per process)
+# ---------------------------------------------------------------------------
+
+_cpp_src = r"""
+torch::Tensor launch_paged_attention_decode(
+    torch::Tensor query,
+    torch::Tensor kv_cache,
+    torch::Tensor block_table,
+    torch::Tensor seq_lens,
+    int B, int H, int Hkv, int D, int P, int max_blocks, float scale);
+"""
+
+_cuda_src = r"""
+#include <cuda_runtime.h>
+#include <cuda_fp16.h>
+#include <cuda_bf16.h>
+#include <cfloat>
+
+#define WARP_SIZE 32
+#define MAX_G 16
+
+extern "C" __global__ void paged_attention_decode_kernel(
+    const __nv_bfloat16* __restrict__ query,
+    const __nv_bfloat16* __restrict__ kv_cache,
+    const int* __restrict__ block_table,
+    const int* __restrict__ seq_lens,
+    __nv_bfloat16* __restrict__ output,
+    int B, int H, int Hkv, int D, int P, int max_blocks, float scale)
+{
+    int linear_bid = blockIdx.x;
+    int b    = linear_bid / Hkv;
+    int kv_h = linear_bid % Hkv;
+    if (b >= B) return;
+
+    int L = seq_lens[b];
+    if (L <= 0) return;
+
+    int num_pages = (L + P - 1) / P;
+    int G = H / Hkv;
+    int tid = threadIdx.x;
+    int num_threads = blockDim.x;
+    int warp_id = tid / WARP_SIZE;
+    int lane_id = tid % WARP_SIZE;
+    int num_warps = num_threads / WARP_SIZE;
+
+    extern __shared__ float smem[];
+    float* scratch = smem;                            // num_warps * G
+    float* weight  = smem + num_warps * G;            // G
+    float* rescale = smem + num_warps * G + G;        // G
+
+    // Load queries for all heads in this KV group into fp32 registers
+    float q_reg[MAX_G];
+    #pragma unroll
+    for (int g = 0; g < G; g++) {
+        int q_h = kv_h * G + g;
+        q_reg[g] = __bfloat162float(query[b * H * D + q_h * D + tid]);
+    }
+
+    // Online softmax state — maintained by lane 0 only
+    float m[MAX_G], l[MAX_G], acc[MAX_G];
+    #pragma unroll
+    for (int g = 0; g < G; g++) {
+        m[g]   = -1e10f;          // effectively -inf for softmax
+        l[g]   = 0.0f;
+        acc[g] = 0.0f;
+    }
+
+    // Pre-compute offsets
+    const int* bt_base = block_table + b * max_blocks;
+    int page_stride  = P * Hkv * 2 * D;      // bytes per page in kv_cache
+    int token_stride = Hkv * 2 * D;           // bytes per token (stride across kv_heads)
+    int k_off = kv_h * 2 * D;                 // offset to K for this kv_head
+    int v_off = k_off + D;                    // offset to V = K + D
+
+    for (int pg = 0; pg < num_pages; pg++) {
+        int block_idx = bt_base[pg];
+        int page_base = block_idx * page_stride;
+        int tokens = (pg == num_pages - 1) ? (L - pg * P) : P;
+
+        for (int t = 0; t < tokens; t++) {
+            int base = page_base + t * token_stride;
+
+            // Coalesced loads: adjacent threads read adjacent bf16 values
+            float k_val = __bfloat162float(kv_cache[base + k_off + tid]);
+            float v_val = __bfloat162float(kv_cache[base + v_off + tid]);
+
+            // ---- Part 1: partial dot products ----
+            float dot[MAX_G];
+            #pragma unroll
+            for (int g = 0; g < G; g++) {
+                dot[g] = q_reg[g] * k_val;
+            }
+
+            // Warp-level butterfly reduction
+            #pragma unroll
+            for (int g = 0; g < G; g++) {
+                #pragma unroll
+                for (int offset = WARP_SIZE / 2; offset > 0; offset >>= 1) {
+                    dot[g] += __shfl_xor_sync(0xffffffff, dot[g], offset);
+                }
+            }
+
+            // Inter-warp reduction: each warp writes its partial to shared memory
+            if (lane_id == 0) {
+                #pragma unroll
+                for (int g = 0; g < G; g++) {
+                    scratch[g * num_warps + warp_id] = dot[g];
+                }
+            }
+            __syncthreads();
+
+            // Warp 0 collates inter-warp partials into full dot products
+            if (warp_id == 0) {
+                #pragma unroll
+                for (int g = 0; g < G; g++) {
+                    float sum = 0.0f;
+                    #pragma unroll
+                    for (int w = 0; w < num_warps; w++) {
+                        sum += scratch[g * num_warps + w];
+                    }
+                    dot[g] = sum * scale;
+                }
+            }
+
+            // ---- Part 2: online softmax (lane 0 of warp 0) ----
+            if (warp_id == 0 && lane_id == 0) {
+                #pragma unroll
+                for (int g = 0; g < G; g++) {
+                    float s = dot[g];
+                    float m_new = fmaxf(m[g], s);
+                    float old_scale = expf(m[g] - m_new);
+                    float exp_val  = expf(s - m_new);
+                    weight[g]  = exp_val;
+                    rescale[g] = old_scale;
+                    l[g] = old_scale * l[g] + exp_val;
+                    m[g] = m_new;
+                }
+            }
+            __syncthreads();
+
+            // ---- Part 3: all threads update

... (5048 more chars)
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py",
  "content": "<10612 chars \u2014 see diff>"
}
tool
stdout (24 chars)
Wrote file successfully.
assistant
Good. CUDA 13.2, SM120, bf16 supported. Now writing the kernel.
assistant
in 464out 3057cache_r 58368cache_w 0
assistant
Now let me test correctness:
assistant
bash
args
{
  "description": "Run check.py correctness test",
  "command": "cd /home/infatoshi/cuda/KernelBench-Hard && /home/infatoshi/.local/bin/uv run python problems/03_paged_attention/check.py 2>&1",
  "timeout": 300000
}
tool
stdout (5141 chars) — TRUNCATED
Traceback (most recent call last):
  File "/home/infatoshi/cuda/KernelBench-Hard/.venv/lib/python3.11/site-packages/torch/utils/cpp_extension.py", line 2774, in _run_ninja_build
    subprocess.run(
  File "/home/infatoshi/.local/share/uv/python/cpython-3.11.15-linux-x86_64-gnu/lib/python3.11/subprocess.py", line 571, in run
    raise CalledProcessError(retcode, process.args,
subprocess.CalledProcessError: Command '['ninja', '-v']' returned non-zero exit status 2.

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/check.py", line 109, in <module>
    main()
  File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/check.py", line 72, in main
    sol_out = sol_model(*inputs)
              ^^^^^^^^^^^^^^^^^^
  File "/home/infatoshi/cuda/KernelBench-Hard/.venv/lib/python3.11/site-packages/torch/nn/modules/module.py", line 1779, in _wrapped_call_impl
    return self._call_impl(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/infatoshi/cuda/KernelBench-Hard/.venv/lib/python3.11/site-packages/torch/nn/modules/module.py", line 1790, in _call_impl
    return forward_call(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py", line 283, in forward
    mod = _get_module()
          ^^^^^^^^^^^^^
  File "/home/infatoshi/cuda/Kernel

... (3641 more chars)
assistant
in 136out 127cache_r 61824cache_w 0
assistant
edit /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
diff (12 lines)
--- a//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
+++ b//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
@@ -208,8 +208,7 @@
     int G           = H / Hkv;
     size_t smem_bytes = (num_warps + 2) * G * sizeof(float);
 
-    auto stream = at::cuda::getCurrentCUDAStream();
-    paged_attention_decode_kernel<<<num_blocks, num_threads, smem_bytes, stream>>>(
+    paged_attention_decode_kernel<<<num_blocks, num_threads, smem_bytes>>>(
         reinterpret_cast<const __nv_bfloat16*>(query.data_ptr<torch::BFloat16>()),
         reinterpret_cast<const __nv_bfloat16*>(kv_cache.data_ptr<torch::BFloat16>()),
         block_table.data_ptr<int>(),
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py",
  "oldString": "<498 chars \u2014 see below>",
  "newString": "<438 chars \u2014 see below>"
}
oldString (498 chars)
    auto stream = at::cuda::getCurrentCUDAStream();
    paged_attention_decode_kernel<<<num_blocks, num_threads, smem_bytes, stream>>>(
        reinterpret_cast<const __nv_bfloat16*>(query.data_ptr<torch::BFloat16>()),
        reinterpret_cast<const __nv_bfloat16*>(kv_cache.data_ptr<torch::BFloat16>()),
        block_table.data_ptr<int>(),
        seq_lens.data_ptr<int>(),
        reinterpret_cast<__nv_bfloat16*>(output.data_ptr<torch::BFloat16>()),
        B, H, Hkv, D, P, max_blocks, scale);
newString (438 chars)
    paged_attention_decode_kernel<<<num_blocks, num_threads, smem_bytes>>>(
        reinterpret_cast<const __nv_bfloat16*>(query.data_ptr<torch::BFloat16>()),
        reinterpret_cast<const __nv_bfloat16*>(kv_cache.data_ptr<torch::BFloat16>()),
        block_table.data_ptr<int>(),
        seq_lens.data_ptr<int>(),
        reinterpret_cast<__nv_bfloat16*>(output.data_ptr<torch::BFloat16>()),
        B, H, Hkv, D, P, max_blocks, scale);
tool
stdout (26 chars)
Edit applied successfully.
assistant
Compilation error — `at::cuda::getCurrentCUDAStream` not found in cuda source. Let me fix the stream API and retry:
assistant
in 1705out 407cache_r 62080cache_w 0
assistant
bash
args
{
  "description": "Retry check.py after stream fix",
  "command": "cd /home/infatoshi/cuda/KernelBench-Hard && /home/infatoshi/.local/bin/uv run python problems/03_paged_attention/check.py 2>&1",
  "timeout": 300000
}
tool
stdout (5 chars)
PASS
assistant
in 64out 124cache_r 64896cache_w 0
assistant
todowrite
args
{
  "todos": [
    {
      "content": "Write initial solution.py with CUDA C++ kernel + C++ wrapper via load_inline",
      "priority": "high",
      "status": "completed"
    },
    {
      "content": "Run check.py for correctness verification",
      "priority": "high",
      "status": "completed"
    },
    {
      "content": "Run benchmark.py for performance measurement",
      "priority": "high",
      "status": "in_progress"
    },
    {
      "content": "Profile with ncu and iterate if performance is below target",
      "priority": "medium",
      "status": "pending"
    }
  ]
}
tool
stdout (417 chars)
content: 'Write initial solution.py with CUDA C++ kernel + C++ wrapper via load_inline'
status: 'completed'
priority: 'high'
content: 'Run check.py for correctness verification'
status: 'completed'
priority: 'high'
content: 'Run benchmark.py for performance measurement'
status: 'in_progress'
priority: 'high'
content: 'Profile with ncu and iterate if performance is below target'
status: 'pending'
priority: 'medium'
assistant
Correctness passes. Now let me benchmark:
assistant
bash
args
{
  "description": "Run benchmark.py for performance",
  "command": "cd /home/infatoshi/cuda/KernelBench-Hard && /home/infatoshi/.local/bin/uv run python problems/03_paged_attention/benchmark.py 2>&1",
  "timeout": 600000
}
tool
stdout (982 chars)
Traceback (most recent call last):
  File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/benchmark.py", line 131, in <module>
    main()
  File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/benchmark.py", line 42, in main
    meta = yaml.safe_load(Path("problem.yaml").read_text())
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/infatoshi/.local/share/uv/python/cpython-3.11.15-linux-x86_64-gnu/lib/python3.11/pathlib.py", line 1058, in read_text
    with self.open(mode='r', encoding=encoding, errors=errors) as f:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/infatoshi/.local/share/uv/python/cpython-3.11.15-linux-x86_64-gnu/lib/python3.11/pathlib.py", line 1044, in open
    return io.open(self, mode, buffering, encoding, errors, newline)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: 'problem.yaml'
assistant
in 32out 275cache_r 65408cache_w 0
assistant
bash
args
{
  "description": "Run benchmark from problem directory",
  "command": "cd /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention && /home/infatoshi/.local/bin/uv run python benchmark.py 2>&1",
  "timeout": 600000
}
tool
stdout (3376 chars) — TRUNCATED
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] Graph break from `Tensor.item()`, consider setting:
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     torch._dynamo.config.capture_scalar_outputs = True
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] or:
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     env TORCHDYNAMO_CAPTURE_SCALAR_OUTPUTS=1
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] to include these operations in the captured graph.
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] Graph break: from user code at:
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]   File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/reference.py", line 89, in forward
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     L = int(seq_lens[b].item())
W0427 09:12:19.341000 1130296 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 
W0427 09

... (1876 more chars)
assistant
in 753out 121cache_r 65408cache_w 0
assistant
read /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py"
}
tool
stdout (12201 chars) — TRUNCATED
<path>/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py</path>
<type>file</type>
<content>
1: """Paged attention decode kernel for RTX PRO 6000 (SM120 Blackwell).
2: 
3: Single-query decode with grouped-query attention (GQA).
4: Uses online softmax to process KV cache in a single pass without gathering pages.
5: One block per (batch, kv_head) pair; each thread handles one head_dim element.
6: """
7: from __future__ import annotations
8: 
9: import math
10: 
11: import torch
12: import torch.nn as nn
13: from torch.utils.cpp_extension import load_inline
14: 
15: OP_TYPE = "attention"
16: SUPPORTED_PRECISIONS = ["bf16"]
17: HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]
18: 
19: # Language-visible shape knobs (overridden by check.py/benchmark.py)
20: BATCH = 8
21: NUM_HEADS = 32
22: NUM_KV_HEADS = 8
23: HEAD_DIM = 128
24: SEQ_LEN = 1024
25: PAGE_SIZE = 16
26: 
27: # ---------------------------------------------------------------------------
28: # CUDA kernel + wrapper (compiled once per process)
29: # ---------------------------------------------------------------------------
30: 
31: _cpp_src = r"""
32: torch::Tensor launch_paged_attention_decode(
33:     torch::Tensor query,
34:     torch::Tensor kv_cache,
35:     torch::Tensor block_table,
36:     torch::Tensor seq_lens,
37:     int B, int H, int Hkv, int D, int P, int max_blocks, float scale);
38: """
39: 
40: _cuda_src = r"""
41: #include <cuda_runtime.h>
42: #include <cuda_fp16.h>
43: #in

... (10701 more chars)
assistant
The performance is terrible — 1.1% peak fraction. The issue is per-token `__syncthreads()` overhead and low occupancy for small batches. Let me redesign with a warp-only kernel (no shared memory, no barriers, everything via warp shuffle):
assistant
in 1276out 120cache_r 66304cache_w 0
assistant
write /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
diff (305 lines — TRUNCATED)
--- a//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
+++ b//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
@@ -1,8 +1,9 @@
 """Paged attention decode kernel for RTX PRO 6000 (SM120 Blackwell).
 
 Single-query decode with grouped-query attention (GQA).
-Uses online softmax to process KV cache in a single pass without gathering pages.
-One block per (batch, kv_head) pair; each thread handles one head_dim element.
+Warp-only kernel: one warp per (batch, kv_head), no shared memory, no barriers.
+Each lane handles D/32 dimensions; all reduction via __shfl_xor_sync.
+Online softmax processes KV cache in a single streaming pass.
 """
 from __future__ import annotations
 
@@ -16,7 +17,6 @@
 SUPPORTED_PRECISIONS = ["bf16"]
 HARDWARE_REQUIRED = ["RTX_PRO_6000", "H100", "B200"]
 
-# Language-visible shape knobs (overridden by check.py/benchmark.py)
 BATCH = 8
 NUM_HEADS = 32
 NUM_KV_HEADS = 8
@@ -41,10 +41,10 @@
 #include <cuda_runtime.h>
 #include <cuda_fp16.h>
 #include <cuda_bf16.h>
-#include <cfloat>
 
 #define WARP_SIZE 32
 #define MAX_G 16
+#define MAX_STRIDE 8  // max D/32 = 128/32 = 4, plus safety
 
 extern "C" __global__ void paged_attention_decode_kernel(
     const __nv_bfloat16* __restrict__ query,
@@ -64,41 +64,56 @@
 
     int num_pages = (L + P - 1) / P;
     int G = H / Hkv;
-    int tid = threadIdx.x;
-    int num_threads = blockDim.x;
-    int warp_id = tid / WARP_SIZE;
-    int lane_id = tid % WARP_SIZE;
-    int num_warps = num_threads / WARP_SIZE;
-
-    extern __shared__ float smem[];
-    float* scratch = smem;                            // num_warps * G
-    float* weight  = smem + num_warps * G;            // G
-    float* rescale = smem + num_warps * G + G;        // G
-
-    // Load queries for all heads in this KV group into fp32 registers
-    float q_reg[MAX_G];
+    int lane_id = threadIdx.x;          // 0..31
+    int stride = D / WARP_SIZE;          // elements per lane per head (4 for D=128, 2 for D=64)
+    unsigned mask = __activemask();
+
+    // ------------------------------------------------------------------
+    // Load queries for all G heads into registers (fp32).
+    // Each lane loads 'stride' elements per query head, stride-separated.
+    // ------------------------------------------------------------------
+    float q_reg[MAX_G][MAX_STRIDE];
     #pragma unroll
     for (int g = 0; g < G; g++) {
         int q_h = kv_h * G + g;
-        q_reg[g] = __bfloat162float(query[b * H * D + q_h * D + tid]);
-    }
-
-    // Online softmax state — maintained by lane 0 only
-    float m[MAX_G], l[MAX_G], acc[MAX_G];
+        int q_base = b * H * D + q_h * D;
+        #pragma unroll
+        for (int s = 0; s < stride; s++) {
+            int idx = q_base + lane_id + s * WARP_SIZE;
+            q_reg[g][s] = __bfloat162float(query[idx]);
+        }
+    }
+
+    // Online softmax state (maintained by lane 0)
+    float m[MAX_G], l[MAX_G];
     #pragma unroll
     for (int g = 0; g < G; g++) {
-        m[g]   = -1e10f;          // effectively -inf for softmax
-        l[g]   = 0.0f;
-        acc[g] = 0.0f;
-    }
-
+        m[g] = -1e10f;
+        l[g] = 0.0f;
+    }
+    // Output accumulator: one float per (g, stride_s)
+    float acc[MAX_G][MAX_STRIDE];
+    #pragma unroll
+    for (int g = 0; g < G; g++) {
+        #pragma unroll
+        for (int s = 0; s < stride; s++) {
+            acc[g][s] = 0.0f;
+        }
+    }
+
+    // ------------------------------------------------------------------
     // Pre-compute offsets
+    // ------------------------------------------------------------------
     const int* bt_base = block_table + b * max_blocks;
-    int page_stride  = P * Hkv * 2 * D;      // bytes per page in kv_cache
-    int token_stride = Hkv * 2 * D;           // bytes per token (stride across kv_heads)
-    int k_off = kv_h * 2 * D;                 // offset to K for this kv_head
-    int v_off = k_off + D;                    // offset to V = K + D
-
+    int page_stride  = P * Hkv * 2 * D;       // bf16 elements per page
+    int token_stride = Hkv * 2 * D;            // bf16 elements per token
+    int head_off = kv_h * 2 * D;               // offset to this KV head's K
+    int k_base = head_off;
+    int v_base = head_off + D;
+
+    // ------------------------------------------------------------------
+    // Main loop: iterate over pages, then tokens
+    // ------------------------------------------------------------------
     for (int pg = 0; pg < num_pages; pg++) {
         int block_idx = bt_base[pg];
         int page_base = block_idx * page_stride;
@@ -107,91 +122,92 @@
         for (int t = 0; t < tokens; t++) {
             int base = page_base + t * token_stride;
 
-            // Coalesced loads: adjacent threads read adjacent bf16 values
-            float k_val = __bfloat162float(kv_cache[base + k_off + tid]);
-            float v_val = __bfloat162float(kv_cache[base + v_off + tid]);
-
-            // ---- Part 1: partial dot products ----
+            // ---- load K and V for this token, strided across lanes ----
+            float k_vals[MAX_STRIDE];
+            float v_vals[MAX_STRIDE];
+            #pragma unroll
+            for (int s = 0; s < stride; s++) {
+                int idx = base + k_base + lane_id + s * WARP_SIZE;
+                k_vals[s] = __bfloat162float(kv_cache[idx]);
+                v_vals[s] = __bfloat162float(kv_cache[base + v_base + lane_id + s * WARP_SIZE]);
+            }
+
+            // ---- compute dot product Q @ K for each query head ----
             float dot[MAX_G];
             #pragma unroll
             for (int g = 0; g < G; g++) {
-                dot[g] = q_reg[g] * k_val;
-            }
-
-            // Warp-level butterfly reduction
+                float s = 0.0f;
+                #pragma unroll
+                for (int j = 0; j < stride; j++) {
+                    s = fmaf(q_reg[g][j], k_vals[j], s);
+          

... (5805 more chars)
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py",
  "content": "<11232 chars \u2014 see diff>"
}
tool
stdout (24 chars)
Wrote file successfully.
assistant
in 10578out 3109cache_r 67456cache_w 0
assistant
edit /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
diff (32 lines)
--- a//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
+++ b//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
@@ -139,7 +139,7 @@
                 float s = 0.0f;
                 #pragma unroll
                 for (int j = 0; j < stride; j++) {
-                    s = fmaf(q_reg[g][j], k_vals[j], s);
+                    s += q_reg[g][j] * k_vals[j];
                 }
                 dot[g] = s;
             }
@@ -156,6 +156,11 @@
 
             // ---- online softmax (lane 0 computes; broadcast via shuffle) ----
             float weight[MAX_G], rescale[MAX_G];
+            #pragma unroll
+            for (int g = 0; g < G; g++) {
+                weight[g]  = 0.0f;
+                rescale[g] = 0.0f;
+            }
             if (lane_id == 0) {
                 #pragma unroll
                 for (int g = 0; g < G; g++) {
@@ -182,7 +187,7 @@
             for (int g = 0; g < G; g++) {
                 #pragma unroll
                 for (int s = 0; s < stride; s++) {
-                    acc[g][s] = fmaf(rescale[g], acc[g][s], weight[g] * v_vals[s]);
+                    acc[g][s] = rescale[g] * acc[g][s] + weight[g] * v_vals[s];
                 }
             }
         }
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py",
  "oldString": "<2022 chars \u2014 see below>",
  "newString": "<2164 chars \u2014 see below>"
}
oldString (2022 chars)
            // ---- compute dot product Q @ K for each query head ----
            float dot[MAX_G];
            #pragma unroll
            for (int g = 0; g < G; g++) {
                float s = 0.0f;
                #pragma unroll
                for (int j = 0; j < stride; j++) {
                    s = fmaf(q_reg[g][j], k_vals[j], s);
                }
                dot[g] = s;
            }

            // Warp-level butterfly sum reduction
            #pragma unroll
            for (int g = 0; g < G; g++) {
                #pragma unroll
                for (int offset = WARP_SIZE / 2; offset > 0; offset >>= 1) {
                    dot[g] += __shfl_xor_sync(mask, dot[g], offset);
                }
                dot[g] *= scale;
            }

            // ---- online softmax (lane 0 computes; broadcast via shuffle) ----
            float weight[MAX_G], rescale[MAX_G];
            if (lane_id == 0) {
                #pragma unroll
                for (int g = 0; g < G; g++) {
                    float s = dot[g];
                    float m_new = fmaxf(m[g], s);
                    float old_scale = __expf(m[g] - m_new);
                    float exp_val   = __expf(s - m_new);
                    weight[g]  = exp_val;
                    rescale[g] = old_scale;
                    l[g] = old_scale * l[g] + exp_val;
                    m[g] = m_new;
                }
            }

            // Broadcast weight and rescale from lane 0 to all lanes
            #pragma unroll
            for (int g = 0; g < G; g++) {
                weight[g]  = __shfl_sync(mask, weight[g],  0);
                rescale[g] = __shfl_sync(mask, rescale[g], 0);
            }

            // ---- all lanes update output accumulator ----
            #pragma unroll
            for (int g = 0; g < G; g++) {
                #pragma unroll
                for (int s = 0; s < stride; s++) {
                    acc[g][s] = fmaf(rescale[g], acc[g][s], weight[g] * v_vals[s]);
                }
            }
newString (2164 chars)
            // ---- compute dot product Q @ K for each query head ----
            float dot[MAX_G];
            #pragma unroll
            for (int g = 0; g < G; g++) {
                float s = 0.0f;
                #pragma unroll
                for (int j = 0; j < stride; j++) {
                    s += q_reg[g][j] * k_vals[j];
                }
                dot[g] = s;
            }

            // Warp-level butterfly sum reduction
            #pragma unroll
            for (int g = 0; g < G; g++) {
                #pragma unroll
                for (int offset = WARP_SIZE / 2; offset > 0; offset >>= 1) {
                    dot[g] += __shfl_xor_sync(mask, dot[g], offset);
                }
                dot[g] *= scale;
            }

            // ---- online softmax (lane 0 computes; broadcast via shuffle) ----
            float weight[MAX_G], rescale[MAX_G];
            #pragma unroll
            for (int g = 0; g < G; g++) {
                weight[g]  = 0.0f;
                rescale[g] = 0.0f;
            }
            if (lane_id == 0) {
                #pragma unroll
                for (int g = 0; g < G; g++) {
                    float s = dot[g];
                    float m_new = fmaxf(m[g], s);
                    float old_scale = __expf(m[g] - m_new);
                    float exp_val   = __expf(s - m_new);
                    weight[g]  = exp_val;
                    rescale[g] = old_scale;
                    l[g] = old_scale * l[g] + exp_val;
                    m[g] = m_new;
                }
            }

            // Broadcast weight and rescale from lane 0 to all lanes
            #pragma unroll
            for (int g = 0; g < G; g++) {
                weight[g]  = __shfl_sync(mask, weight[g],  0);
                rescale[g] = __shfl_sync(mask, rescale[g], 0);
            }

            // ---- all lanes update output accumulator ----
            #pragma unroll
            for (int g = 0; g < G; g++) {
                #pragma unroll
                for (int s = 0; s < stride; s++) {
                    acc[g][s] = rescale[g] * acc[g][s] + weight[g] * v_vals[s];
                }
            }
tool
stdout (26 chars)
Edit applied successfully.
assistant
Let me fix two issues — `fmaf` may not be available in CUDA device code, and uninitialized broadcast values. Also I should ensure `stride` is correct for D=64:
assistant
in 94out 1271cache_r 81152cache_w 0
assistant
bash
args
{
  "description": "Check correctness then benchmark",
  "command": "cd /home/infatoshi/cuda/KernelBench-Hard && uv run python problems/03_paged_attention/check.py 2>&1 && echo \"---\" && cd /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention && uv run python benchmark.py 2>&1",
  "timeout": 600000
}
tool
stdout (3385 chars) — TRUNCATED
PASS
---
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] Graph break from `Tensor.item()`, consider setting:
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     torch._dynamo.config.capture_scalar_outputs = True
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] or:
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     env TORCHDYNAMO_CAPTURE_SCALAR_OUTPUTS=1
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] to include these operations in the captured graph.
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] Graph break: from user code at:
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]   File "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/reference.py", line 89, in forward
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0]     L = int(seq_lens[b].item())
W0427 09:18:45.298000 1130835 .venv/lib/python3.11/site-packages/torch/_dynamo/variables/tensor.py:1379] [0/0] 

... (1885 more chars)
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in 15out 148cache_r 84480cache_w 0
assistant
write /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
diff (299 lines — TRUNCATED)
--- a//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
+++ b//home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py
@@ -1,7 +1,7 @@
 """Paged attention decode kernel for RTX PRO 6000 (SM120 Blackwell).
 
 Single-query decode with grouped-query attention (GQA).
-Warp-only kernel: one warp per (batch, kv_head), no shared memory, no barriers.
+One 32-thread warp-block per query head for maximum parallelism.
 Each lane handles D/32 dimensions; all reduction via __shfl_xor_sync.
 Online softmax processes KV cache in a single streaming pass.
 """
@@ -25,7 +25,7 @@
 PAGE_SIZE = 16
 
 # ---------------------------------------------------------------------------
-# CUDA kernel + wrapper (compiled once per process)
+# CUDA kernel + wrapper
 # ---------------------------------------------------------------------------
 
 _cpp_src = r"""
@@ -43,8 +43,7 @@
 #include <cuda_bf16.h>
 
 #define WARP_SIZE 32
-#define MAX_G 16
-#define MAX_STRIDE 8  // max D/32 = 128/32 = 4, plus safety
+#define MAX_STRIDE 8
 
 extern "C" __global__ void paged_attention_decode_kernel(
     const __nv_bfloat16* __restrict__ query,
@@ -52,68 +51,49 @@
     const int* __restrict__ block_table,
     const int* __restrict__ seq_lens,
     __nv_bfloat16* __restrict__ output,
-    int B, int H, int Hkv, int D, int P, int max_blocks, float scale)
+    int B, int H, int Hkv, int D, int P, int max_blocks, float scale,
+    int G)
 {
+    // One block per query head
     int linear_bid = blockIdx.x;
-    int b    = linear_bid / Hkv;
-    int kv_h = linear_bid % Hkv;
+    int b      = linear_bid / H;
+    int q_head = linear_bid % H;
     if (b >= B) return;
 
     int L = seq_lens[b];
     if (L <= 0) return;
 
+    int kv_h = q_head / G;   // which KV head this query head maps to
     int num_pages = (L + P - 1) / P;
-    int G = H / Hkv;
-    int lane_id = threadIdx.x;          // 0..31
-    int stride = D / WARP_SIZE;          // elements per lane per head (4 for D=128, 2 for D=64)
+    int lane_id = threadIdx.x;
+    int stride  = D / WARP_SIZE;
     unsigned mask = __activemask();
 
-    // ------------------------------------------------------------------
-    // Load queries for all G heads into registers (fp32).
-    // Each lane loads 'stride' elements per query head, stride-separated.
-    // ------------------------------------------------------------------
-    float q_reg[MAX_G][MAX_STRIDE];
+    // Load this query head (fp32)
+    float q_val[MAX_STRIDE];
+    int q_base = b * H * D + q_head * D;
     #pragma unroll
-    for (int g = 0; g < G; g++) {
-        int q_h = kv_h * G + g;
-        int q_base = b * H * D + q_h * D;
-        #pragma unroll
-        for (int s = 0; s < stride; s++) {
-            int idx = q_base + lane_id + s * WARP_SIZE;
-            q_reg[g][s] = __bfloat162float(query[idx]);
-        }
-    }
-
-    // Online softmax state (maintained by lane 0)
-    float m[MAX_G], l[MAX_G];
+    for (int s = 0; s < stride; s++) {
+        q_val[s] = __bfloat162float(query[q_base + lane_id + s * WARP_SIZE]);
+    }
+
+    // Online softmax state for this single query head
+    float m = -1e10f;
+    float l = 0.0f;
+    float acc[MAX_STRIDE];
     #pragma unroll
-    for (int g = 0; g < G; g++) {
-        m[g] = -1e10f;
-        l[g] = 0.0f;
-    }
-    // Output accumulator: one float per (g, stride_s)
-    float acc[MAX_G][MAX_STRIDE];
-    #pragma unroll
-    for (int g = 0; g < G; g++) {
-        #pragma unroll
-        for (int s = 0; s < stride; s++) {
-            acc[g][s] = 0.0f;
-        }
-    }
-
-    // ------------------------------------------------------------------
-    // Pre-compute offsets
-    // ------------------------------------------------------------------
+    for (int s = 0; s < stride; s++) {
+        acc[s] = 0.0f;
+    }
+
+    // Offsets into kv_cache for this KV head
     const int* bt_base = block_table + b * max_blocks;
-    int page_stride  = P * Hkv * 2 * D;       // bf16 elements per page
-    int token_stride = Hkv * 2 * D;            // bf16 elements per token
-    int head_off = kv_h * 2 * D;               // offset to this KV head's K
-    int k_base = head_off;
-    int v_base = head_off + D;
-
-    // ------------------------------------------------------------------
-    // Main loop: iterate over pages, then tokens
-    // ------------------------------------------------------------------
+    int page_stride  = P * Hkv * 2 * D;
+    int token_stride = Hkv * 2 * D;
+    int k_off = kv_h * 2 * D;
+    int v_off = k_off + D;
+
+    // Main loop over pages and tokens
     for (int pg = 0; pg < num_pages; pg++) {
         int block_idx = bt_base[pg];
         int page_base = block_idx * page_stride;
@@ -122,92 +102,58 @@
         for (int t = 0; t < tokens; t++) {
             int base = page_base + t * token_stride;
 
-            // ---- load K and V for this token, strided across lanes ----
+            // Load K and V values for this token (strided across lanes)
             float k_vals[MAX_STRIDE];
             float v_vals[MAX_STRIDE];
             #pragma unroll
             for (int s = 0; s < stride; s++) {
-                int idx = base + k_base + lane_id + s * WARP_SIZE;
-                k_vals[s] = __bfloat162float(kv_cache[idx]);
-                v_vals[s] = __bfloat162float(kv_cache[base + v_base + lane_id + s * WARP_SIZE]);
-            }
-
-            // ---- compute dot product Q @ K for each query head ----
-            float dot[MAX_G];
-            #pragma unroll
-            for (int g = 0; g < G; g++) {
-                float s = 0.0f;
-                #pragma unroll
-                for (int j = 0; j < stride; j++) {
-                    s += q_reg[g][j] * k_vals[j];
-                }
-                dot[g] = s;
-            }
-
-            // Warp-level butterfly sum reduction
-            #pragma unroll
-            for (int g = 0; g < G; g++) {
-                #pragma unroll
-     

... (5201 more chars)
args
{
  "filePath": "/home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention/solution.py",
  "content": "<8857 chars \u2014 see diff>"
}
tool
stdout (24 chars)
Wrote file successfully.
assistant
The warp-only kernel didn't help. The problem is occupancy — with B*Hkv blocks and only 1 warp each, we have too few blocks for small batch sizes. Let me switch to B*H blocks (one per query head) which gives G× more parallelism. The KV cache will be re-read G times but this matches what the reference does after `repeat_interleave`.
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in 1326out 2636cache_r 84608cache_w 0
assistant
bash
args
{
  "description": "Clean build cache, test correctness, benchmark",
  "command": "rm -rf /home/infatoshi/.cache/torch_extensions/py311_cu130/paged_attention_decode_ext && cd /home/infatoshi/cuda/KernelBench-Hard && uv run python problems/03_paged_attention/check.py 2>&1 && echo \"---BENCH---\" && cd /home/infatoshi/cuda/KernelBench-Hard/problems/03_paged_attention && uv run python benchmark.py 2>&1",
  "timeout": 600000
}
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in 18out 184cache_r 97280cache_w 0