GQA ragged prefill causal h32 kv8 d64
8 eligible runs
gqa-ragged-attention
Batched Grouped Query Attention prefill with ragged (variable-length) inputs. Causal mask is applied. Captured from Llama-3.2-1B during total prefill.
Source baseline · unbeaten
8.93µsmean
flashinfer / wrapper44b034FlashInfer-Bench baselines · Apache-2.0 · python
Reported evidence · last observed 2026-04-20. The source's designated baseline implementation. Reported by source; not independently reproduced.
Current records
Workloadtotal_q = 1 · total_kv = 1 · len_indptr = 2 · bf16total_q = 13716 · total_kv = 13716 · len_indptr = 32 · bf16total_q = 35 · total_kv = 35 · len_indptr = 2 · bf16total_q = 5932 · total_kv = 5932 · len_indptr = 13 · bf16total_q = 10930 · total_kv = 10930 · len_indptr = 55 · bf16total_q = 8819 · total_kv = 8819 · len_indptr = 10 · bf16
Not measured on H100 for this workload. Challenges →
Source-native comparison · GPU NVIDIA B200 · Workload total_q = 1 · total_kv = 1 · len_indptr = 2 · bf16 · CUDA 13.0 · Framework pytorch 2.11.0+cu130 · Protocol flashinfer-bench · mean · 2 results · last observed 2026-04-20Record history →
Estimated floor 1 ns · record 11601.3× above itestimate, not evidence ›
DRAM 1 ns · bandwidth-bound on B200
every declared tensor crosses HBM exactly once (8,000 GB/s, B200 datasheet)
no arithmetic formula for this family: bandwidth floor only
headroom-v1: a lower bound from declared tensors and datasheet peaks. A kernel can sit well above it for good reasons.
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Implementation
Latency
vs #1
Trust
Observed
18.93µs1.00×Reported · Apache-2.0 · source2026-04-20
Measured exactly what you asked. The source's designated baseline implementation. Reported by source; not independently reproduced.
source mirroredApache-2.0no install recipeView source →Run detail →
28.99µs1.01×Reported · Apache-2.0 · source2026-04-20
Measured exactly what you asked. The source's designated baseline implementation. Reported by source; not independently reproduced.
source mirroredApache-2.0no install recipeView source →Run detail →
Implementations
Implementation
Runtime
Best latency
Evidence
Availability
Semantics
Inputs and outputs
qbf16 [total_q, num_qo_heads, head_dim]
kbf16 [total_kv, num_kv_heads, head_dim]
vbf16 [total_kv, num_kv_heads, head_dim]
qo_indptrint32 [len_indptr]
kv_indptrint32 [len_indptr]
sm_scalefp32 scalar
outputbf16 [total_q, num_qo_heads, head_dim]
lsefp32 [total_q, num_qo_heads]
Axes and behavior
total_qvariable
head_dimconstant = 64
total_kvvariable
len_indptrvariable
num_kv_headsconstant = 8
num_qo_headsconstant = 32
determinismunspecified
constraintsNo mutation or aliasing
Identity
Sources: FlashInfer-Bench (2026-04-20) · Apache-2.0last observed 2026-04-20How records are decidedJSON