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[https://nvbugs/6270671][fix] Replace the hardcoded multiBlock=1 with a call to… #15312

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Merged
pengbowang-nv merged 2 commits into from
Jun 17, 2026
Merged

[https://nvbugs/6270671][fix] Replace the hardcoded multiBlock=1 with a call to… #15312

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a910d86
[nvbugs/6270671][fix] Enable multi-block mode for BF16 spec-dec XQA k…
tensorrt-cicd Jun 12, 2026
0474212
rename multiblock calc functions
pengbowang-nv Jun 16, 2026
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14 changes: 9 additions & 5 deletions cpp/tensorrt_llm/kernels/decoderMaskedMultiheadAttention/decoderXQARunner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -462,10 +462,14 @@ void DecoderXQARunner::runImpl(XQAParams const& xqaParams, KVCacheBuffer const&
appendParam(&launchParams.scratch);

uint32_t multiBlock = 1;
// if (xqaParams.multi_block_mode)
// {
// multiBlock = computeMultiBlockCount(xqaParams, xqaParams.batch_size, multiprocessorCount);
// }
if (xqaParams.multi_block_mode)
{
// HMMA spec-dec gridDim is {multiBlock, nbKVHeads * nbTokenBlocksPerGrp, batchSize};
// mirror the GMMA spec-dec wave-count tuning by passing nbTokenBlocksPerGrp where the GMMA
// path passes specDecBlocks (singleBlockCount factor along the head/q-token axis).
multiBlock = computeMultiBlockCountSpecDec(
xqaParams, xqaParams.batch_size, multiprocessorCount, nbTokenBlocksPerGrp);
}
auto const gridDim = (dim3{multiBlock, xqaParams.num_kv_heads * nbTokenBlocksPerGrp, xqaParams.batch_size});
dim3 const blockDim(128, 1, 2);

Expand Down Expand Up @@ -536,7 +540,7 @@ void DecoderXQARunner::runImpl(XQAParams const& xqaParams, KVCacheBuffer const&
{
if (isSpecDec && isGMMAKernel)
{
multiBlock = computeMultiBlockCountSpecDecGMMA(
multiBlock = computeMultiBlockCountSpecDec(
xqaParams, xqaParams.batch_size, multiprocessorCount, specDecBlocks);
}
else if (!isSpecDec)
Expand Down
2 changes: 1 addition & 1 deletion cpp/tensorrt_llm/kernels/decoderMaskedMultiheadAttention/decoderXQARunnerUtils.h
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Original file line number Diff line number Diff line change
Expand Up @@ -442,7 +442,7 @@ inline int computeMultiBlockCountForMLA(XQAParams const& xqaParams, int multipro
return 1; // disable multi-block for MLA kernel for now.
}

inline int computeMultiBlockCountSpecDecGMMA(
inline int computeMultiBlockCountSpecDec(
XQAParams const& xqaParams, int batchSize, int multiprocessorCount, int specDecBlocks)
{
auto const userSpecified = tensorrt_llm::common::getEnvXqaBlocksPerSequence();
Expand Down
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