TensorRT-LLMs/cpp/tensorrt_llm/kernels/speculativeDecoding/common.cu
Robin Kobus 6d4b045d1f
refactor: Remove enforced sorted order of batch slots (#3502)
Signed-off-by: Robin Kobus <19427718+Funatiq@users.noreply.github.com>
2025-07-14 17:23:02 +02:00

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/*
* Copyright (c) 2024, NVIDIA CORPORATION. All rights reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "tensorrt_llm/common/assert.h"
#include "tensorrt_llm/common/cudaTypeUtils.cuh"
#include "tensorrt_llm/common/cudaUtils.h"
#include "tensorrt_llm/common/memoryUtils.h"
#include "tensorrt_llm/common/reduceKernelUtils.cuh"
#include "tensorrt_llm/common/workspace.h"
#include "tensorrt_llm/kernels/samplingTopPKernels.h"
#include "tensorrt_llm/kernels/speculativeDecoding/common.h"
#include "tensorrt_llm/runtime/runtimeKernels.h"
#ifndef CUDART_VERSION
#error CUDART_VERSION Undefined!
#elif (CUDART_VERSION >= 11050)
#include <cub/cub.cuh>
#else
#include "3rdparty/cub/cub.cuh"
#endif
using namespace tensorrt_llm::common;
using namespace tensorrt_llm::runtime;
namespace tensorrt_llm::kernels::speculative_decoding
{
template <int32_t BLOCK_SIZE>
__global__ void packAcceptedPaths(SizeType32* acceptedLengthsCumSum, SizeType32* pathsOffsets,
SizeType32 const* acceptedLengths, SizeType32 const* bestPathIds, SizeType32 const* paths,
SizeType32 const* batchSlots, SizeType32 batchSize, SizeType32 engineBatchSize, SizeType32 numPaths,
SizeType32 maxPathLen, bool isPathsSeqSlotIdx)
{
// Specialize BlockScan for a 1D block of 128 threads of type int
typedef cub::BlockScan<SizeType32, BLOCK_SIZE> BlockScan;
// Allocate shared memory for BlockScan
__shared__ typename BlockScan::TempStorage tempStorage;
auto const batchSizeRounded = ((engineBatchSize + BLOCK_SIZE - 1) / BLOCK_SIZE) * BLOCK_SIZE;
__shared__ SizeType32 currentCumSum;
__shared__ SizeType32 currentValidIdx;
if (threadIdx.x == 0)
{
currentCumSum = 0;
currentValidIdx = 0;
}
__syncthreads();
for (auto bi = static_cast<SizeType32>(threadIdx.x); bi < batchSizeRounded;
bi += static_cast<SizeType32>(blockDim.x))
{
auto valid = bi < engineBatchSize;
auto const batchSlot = valid ? batchSlots[bi] : 0;
if (batchSlot < 0)
{
valid = false;
}
auto const acceptedLen = valid ? acceptedLengths[batchSlot] - 1 : 0;
SizeType32 cumSum;
BlockScan(tempStorage).ExclusiveSum(acceptedLen + currentCumSum, cumSum);
__syncthreads();
SizeType32 validIndex;
BlockScan(tempStorage).ExclusiveSum(static_cast<SizeType32>(valid) + currentValidIdx, validIndex);
if (threadIdx.x == blockDim.x - 1)
{
currentCumSum = cumSum;
currentValidIdx = validIndex;
}
__syncthreads();
auto const pathBatchIdx = isPathsSeqSlotIdx ? bi : batchSlot;
if (valid)
{
acceptedLengthsCumSum[validIndex] = cumSum;
auto const bestPathIdx = bestPathIds[pathBatchIdx];
auto const pathIdx = flat_index3(pathBatchIdx, bestPathIdx, 0, numPaths, maxPathLen);
for (SizeType32 ti = 0; ti < acceptedLen; ++ti)
{
pathsOffsets[cumSum + ti] = paths[pathIdx + ti + 1] - 1;
}
}
}
if (threadIdx.x == 0)
{
acceptedLengthsCumSum[batchSize] = currentCumSum;
}
}
void invokePackAcceptedPaths(SizeType32* acceptedLengthsCumSum, SizeType32* pathsOffsets,
SizeType32 const* acceptedLengths, SizeType32 const* bestPathIds, SizeType32 const* paths,
SizeType32 const* batchSlots, SizeType32 batchSize, SizeType32 engineBatchSize, SizeType32 numPaths,
SizeType32 maxPathLen, bool isPathsSeqSlotIdx, cudaStream_t stream)
{
constexpr SizeType32 BLOCK_SIZE = 1024;
packAcceptedPaths<BLOCK_SIZE><<<1, BLOCK_SIZE, 0, stream>>>(acceptedLengthsCumSum, pathsOffsets, acceptedLengths,
bestPathIds, paths, batchSlots, batchSize, engineBatchSize, numPaths, maxPathLen, isPathsSeqSlotIdx);
}
namespace
{
__device__ __forceinline__ int4 reduceMaxInt4(int4 const& a, int4 const& b)
{
return a.x >= b.x ? a : b;
}
template <typename T, SizeType32 BLOCK_SIZE>
__global__ void acceptDraftTokensByIdsWithPaths(TokenIdType* outputIds, TokenIdType const* draftIds,
TokenIdType const* targetIds, SizeType32* sequenceLengths, SizeType32* acceptedLengths,
FinishedState* finishedFinal, SizeType32 const* batchSlots, SizeType32 const* paths, TokenIdType const* endIds,
T const** medusaLogits, T const** logitsPtrs, SizeType32* curTokensPerStep, SizeType32 const* targetTokensPerStep,
SizeType32* bestPathIds, SizeType32 vocabSize, SizeType32 maxSeqLen, SizeType32 maxDraftPathLen,
SizeType32 maxDecodingTokens)
{
auto const batchIdx = static_cast<SizeType32>(blockIdx.x);
auto const batchSlot = batchSlots == nullptr ? batchIdx : batchSlots[batchIdx];
auto const inputLength = sequenceLengths == nullptr ? 0 : sequenceLengths[batchSlot];
auto const endId = endIds == nullptr ? -1 : endIds[batchSlot];
auto const numTokensPerStep = curTokensPerStep == nullptr ? maxDecodingTokens : curTokensPerStep[batchSlot];
auto const maxPathLen = maxDraftPathLen + 1;
int4 partialMax{-1, -1, 0, 0};
// Go over different paths and construct implicit sequences
for (auto pathIdx = static_cast<SizeType32>(threadIdx.x); pathIdx < maxDecodingTokens;
pathIdx += static_cast<SizeType32>(blockDim.x))
{
auto acceptedLength = maxPathLen;
auto const pathOffset = flat_index3(batchSlot, pathIdx, 0, maxDecodingTokens, maxPathLen);
bool hasEnd = false;
auto const tokenId = paths[pathOffset];
// Continue if path does not exist
if (tokenId == -1)
{
continue;
}
auto const targetTokenIdx = batchSlot * maxDecodingTokens + tokenId;
auto targetToken = targetIds[targetTokenIdx];
auto nextIdx = tokenId;
// Go along the path
for (SizeType32 ti = 1; ti < maxPathLen; ++ti)
{
auto const tokenId = paths[pathOffset + ti];
// Break if path terminates
if (tokenId == -1)
{
hasEnd = endIds == nullptr ? false
: targetToken == endId; // check if last token is EOS when path terminates.
acceptedLength = hasEnd ? ti - 1 : ti;
break;
}
auto const targetTokenIdx = batchSlot * maxDecodingTokens + tokenId;
auto const draftTokenIdx = batchSlot * (maxDecodingTokens - 1) + tokenId - 1;
// In context phase, no draft tokens are given. Set draft token to -1 to get guaranteed rejection
auto const draftToken = tokenId >= numTokensPerStep ? -1 : draftIds[draftTokenIdx];
// Check if draft tokens are the same as target tokens
bool const accepted = draftToken == targetToken;
hasEnd = endIds == nullptr ? false : targetToken == endId;
if (!accepted || hasEnd)
{
acceptedLength = hasEnd ? ti - 1 : ti;
break;
}
targetToken = targetIds[targetTokenIdx];
nextIdx = tokenId;
}
// Get longest path of the thread
if (partialMax.x < acceptedLength)
{
partialMax.x = acceptedLength;
partialMax.y = pathIdx;
partialMax.z = hasEnd;
partialMax.w = nextIdx;
}
}
// Get the longest path of the block (request)
typedef cub::BlockReduce<int4, BLOCK_SIZE> BlockReduce;
__shared__ typename BlockReduce::TempStorage tempStorage;
int4 total = BlockReduce(tempStorage).Reduce(partialMax, reduceMaxInt4);
__shared__ int4 totalShared;
if (threadIdx.x == 0)
{
totalShared = total;
}
__syncthreads();
auto const acceptedLength = totalShared.x;
auto const bestPathIdx = totalShared.y;
auto const bestNextIdx = numTokensPerStep == 1 ? 0 : totalShared.w;
auto const pathOffset = flat_index3(batchSlot, bestPathIdx, 0, maxDecodingTokens, maxPathLen);
for (auto ti = static_cast<SizeType32>(threadIdx.x); ti < acceptedLength; ti += static_cast<SizeType32>(blockDim.x))
{
auto const tokenId = paths[pathOffset + ti];
auto const targetSrcTokenIdx = batchSlot * maxDecodingTokens + tokenId;
auto const outputTokenIdx = batchSlot * maxSeqLen + inputLength + ti;
auto const targetToken = targetIds[targetSrcTokenIdx];
// Copy accepted tokens to the sequence with draft tokens (outputIds === outputIds)
outputIds[outputTokenIdx] = targetToken;
}
// Leading thread reconstructs winning path and sets new data
if (threadIdx.x == 0)
{
auto const hasEnd = totalShared.z;
// Set end condition
if (hasEnd && finishedFinal)
{
finishedFinal[batchSlot].setFinishedEOS();
}
// Make correction to the sequence length
if (sequenceLengths)
{
sequenceLengths[batchSlot] += acceptedLength;
}
acceptedLengths[batchSlot] = acceptedLength;
// In Medusa decoding step, number of draft tokens is 0 and must be updated for the next steps
if (curTokensPerStep && targetTokensPerStep && numTokensPerStep == 1)
{
curTokensPerStep[batchSlot] = targetTokensPerStep[batchSlot];
}
bestPathIds[batchSlot] = bestPathIdx;
}
// Prepare logits pointers to respective logits from Medusa Heads for the all-top-K sampling kernel
if (medusaLogits && logitsPtrs)
{
for (auto hi = static_cast<SizeType32>(threadIdx.x); hi < maxDraftPathLen;
hi += static_cast<SizeType32>(blockDim.x))
{
logitsPtrs[batchIdx * maxDraftPathLen + hi]
= medusaLogits[batchSlot * maxDraftPathLen + hi] + flat_index2(bestNextIdx, 0, vocabSize);
}
}
}
} // namespace
template <typename T>
void acceptDraftTokensByIdsWithPaths(AcceptDraftTokensByIdsWithPathsParams<T> const& params)
{
SizeType32 constexpr BLOCK_SIZE = 256;
dim3 block(BLOCK_SIZE);
dim3 grid(params.batchSize);
acceptDraftTokensByIdsWithPaths<T, BLOCK_SIZE><<<grid, block, 0, params.stream>>>(params.outputIds, params.draftIds,
params.targetIds, params.sequenceLengths, params.acceptedLengths, params.finishedFinal, params.batchSlots,
params.paths, params.endIds, params.medusaLogits, params.logitsPtrs, params.curTokensPerStep,
params.targetTokensPerStep, params.bestPathIds, params.vocabSize, params.maxSeqLen, params.maxDraftPathLen,
params.maxDecodingTokens);
}
template void acceptDraftTokensByIdsWithPaths(AcceptDraftTokensByIdsWithPathsParams<float> const& params);
template void acceptDraftTokensByIdsWithPaths(AcceptDraftTokensByIdsWithPathsParams<__half> const& params);
namespace
{
template <typename T>
__global__ void maskLogitsBasedOnEntropyKernel(T** logitsPtrs, TokenIdType** outputIdsPtrs, bool* skipDecode,
TokenIdType* outputIds, float* runtimeMultinomialTopP, T const* probsPtr, float const* entropies,
SizeType32 const* generationLengths, float const* posteriorThresholds, float const* posteriorAlphas,
float const* temperatures, SizeType32 const* batchSlots, SizeType32 batchSize, SizeType32 maxDecodingTokens,
SizeType32 vocabSize)
{
auto const tix = blockIdx.z * blockDim.x + threadIdx.x;
auto const batchIdx = static_cast<SizeType32>(blockIdx.x);
auto const tokenIdx = static_cast<SizeType32>(blockIdx.y);
auto const vocabIdx = static_cast<SizeType32>(tix);
auto const batchSlot = batchSlots == nullptr ? batchIdx : batchSlots[batchIdx];
auto const valid = tokenIdx < generationLengths[batchSlot] && vocabIdx < vocabSize;
if (vocabIdx == 0)
{
skipDecode[batchIdx * maxDecodingTokens + tokenIdx] = !valid;
outputIdsPtrs[batchIdx * maxDecodingTokens + tokenIdx] = outputIds + batchIdx * maxDecodingTokens + tokenIdx;
if (temperatures[batchSlot] < 1e-6f)
{
// Greedy sampling with temp = 0.
runtimeMultinomialTopP[batchSlot * maxDecodingTokens + tokenIdx] = 0.f;
}
else
{
runtimeMultinomialTopP[batchSlot * maxDecodingTokens + tokenIdx] = 1.f;
}
}
if (!valid)
{
return;
}
auto const posteriorThreshold = posteriorThresholds[batchSlot];
auto const posteriorAlpha = posteriorAlphas[batchSlot];
auto const entropy = entropies[batchSlot * maxDecodingTokens + tokenIdx];
auto const prob = static_cast<float>(probsPtr[(batchSlot * maxDecodingTokens + tokenIdx) * vocabSize + vocabIdx]);
auto const threshold = min(posteriorThreshold, posteriorAlpha * expf(-entropy));
if (prob < threshold)
{
logitsPtrs[batchIdx * maxDecodingTokens + tokenIdx][vocabIdx] = -FLT_MAX;
}
}
} // namespace
template <typename T>
void maskLogitsBasedOnEntropy(T** logitsPtrs, TokenIdType** outputIdsPtrs, bool* skipDecode, TokenIdType* outputIds,
float* runtimeMultinomialTopP, T const* probsPtr, float const* entropies, SizeType32 const* generationLengths,
float const* posteriorThresholds, float const* posteriorAlphas, float const* temperatures,
SizeType32 const* batchSlots, SizeType32 batchSize, SizeType32 maxDecodingTokens, SizeType32 vocabSize,
cudaStream_t stream)
{
SizeType32 constexpr BLOCK_SIZE = 512;
SizeType32 numBlocks = divUp(vocabSize, BLOCK_SIZE);
dim3 grid(batchSize, maxDecodingTokens, numBlocks);
maskLogitsBasedOnEntropyKernel<<<grid, BLOCK_SIZE, 0, stream>>>(logitsPtrs, outputIdsPtrs, skipDecode, outputIds,
runtimeMultinomialTopP, probsPtr, entropies, generationLengths, posteriorThresholds, posteriorAlphas,
temperatures, batchSlots, batchSize, maxDecodingTokens, vocabSize);
}
template void maskLogitsBasedOnEntropy(float** logitsPtrs, TokenIdType** outputIdsPtrs, bool* skipDecode,
TokenIdType* outputIds, float* runtimeMultinomialTopP, float const* probsPtr, float const* entropies,
SizeType32 const* generationLengths, float const* posteriorThresholds, float const* posteriorAlphas,
float const* temperatures, SizeType32 const* batchSlots, SizeType32 batchSize, SizeType32 maxDecodingTokens,
SizeType32 vocabSize, cudaStream_t stream);
template void maskLogitsBasedOnEntropy(half** logitsPtrs, TokenIdType** outputIdsPtrs, bool* skipDecode,
TokenIdType* outputIds, float* runtimeMultinomialTopP, half const* probsPtr, float const* entropies,
SizeType32 const* generationLengths, float const* posteriorThresholds, float const* posteriorAlphas,
float const* temperatures, SizeType32 const* batchSlots, SizeType32 batchSize, SizeType32 maxDecodingTokens,
SizeType32 vocabSize, cudaStream_t stream);
template <typename T>
void typicalAcceptanceSampling(TypicalAcceptanceSampling<T> const& params, cudaStream_t stream)
{
int8_t* workspaceBytePtr = reinterpret_cast<int8_t*>(params.workspace);
size_t offset{0};
int8_t* samplingWorkspace
= reinterpret_cast<int8_t*>(tensorrt_llm::common::nextWorkspacePtr(workspaceBytePtr, offset,
tensorrt_llm::kernels::getAirTopPWorkspaceSize<T>(
params.batchSize * params.maxDecodingTokens, params.vocabSize, /* isDeterministic */ true)));
float* entropy = reinterpret_cast<float*>(tensorrt_llm::common::nextWorkspacePtr(
workspaceBytePtr, offset, params.batchSize * params.maxDecodingTokens * sizeof(float)));
float* runtimeMultinomialTopP = reinterpret_cast<float*>(tensorrt_llm::common::nextWorkspacePtr(
workspaceBytePtr, offset, params.batchSize * params.maxDecodingTokens * sizeof(float)));
T* probs = reinterpret_cast<T*>(tensorrt_llm::common::nextWorkspacePtr(
workspaceBytePtr, offset, params.batchSize * params.maxDecodingTokens * params.vocabSize * sizeof(T)));
TokenIdType** outputIdsPtrs = reinterpret_cast<TokenIdType**>(tensorrt_llm::common::nextWorkspacePtr(
workspaceBytePtr, offset, params.batchSize * params.maxDecodingTokens * sizeof(TokenIdType*)));
bool* skipDecodePtr = reinterpret_cast<bool*>(tensorrt_llm::common::nextWorkspacePtr(
workspaceBytePtr, offset, params.batchSize * params.maxDecodingTokens * sizeof(bool)));
// compute probs and entropy
{
BiasSoftmaxParams<T> biasSoftmaxParams;
biasSoftmaxParams.logitsPtrs = params.logitsPtrs;
biasSoftmaxParams.probs = probs;
biasSoftmaxParams.outputEntropy = entropy;
biasSoftmaxParams.temperatures = params.temperatures;
biasSoftmaxParams.beamWidths = params.generationLengths;
biasSoftmaxParams.batchSlots = params.batchSlots;
biasSoftmaxParams.batchSize = params.batchSize;
biasSoftmaxParams.maxBatchSize = params.batchSize;
biasSoftmaxParams.maxBeamWidth = params.maxDecodingTokens;
biasSoftmaxParams.vocabSize = params.vocabSize;
biasSoftmaxParams.vocabSizePadded = params.vocabSize;
biasSoftmaxParams.skipSoftMax = false;
biasSoftmaxParams.batchSlotsLogits = false;
biasSoftmaxParams.ptrsForBeams = true;
biasSoftmaxParams.checkParams();
invokeAddBiasSoftMax(biasSoftmaxParams, stream);
sync_check_cuda_error(stream);
}
// correct logits based on the probs and entropy
{
maskLogitsBasedOnEntropy(params.logitsPtrs, outputIdsPtrs, skipDecodePtr, params.outputIds,
runtimeMultinomialTopP, probs, entropy, params.generationLengths, params.posteriorThresholds,
params.posteriorAlphas, params.temperatures, params.batchSlots, params.batchSize, params.maxDecodingTokens,
params.vocabSize, stream);
sync_check_cuda_error(stream);
}
// compute probs of the corrected logits
{
BiasSoftmaxParams<T> biasSoftmaxParams;
biasSoftmaxParams.logitsPtrs = params.logitsPtrs;
biasSoftmaxParams.probs = probs;
biasSoftmaxParams.beamWidths = params.generationLengths;
biasSoftmaxParams.batchSlots = params.batchSlots;
biasSoftmaxParams.batchSize = params.batchSize;
biasSoftmaxParams.maxBatchSize = params.batchSize;
biasSoftmaxParams.maxBeamWidth = params.maxDecodingTokens;
biasSoftmaxParams.vocabSize = params.vocabSize;
biasSoftmaxParams.vocabSizePadded = params.vocabSize;
biasSoftmaxParams.skipSoftMax = false;
biasSoftmaxParams.batchSlotsLogits = false;
biasSoftmaxParams.ptrsForBeams = true;
biasSoftmaxParams.checkParams();
invokeAddBiasSoftMax(biasSoftmaxParams, stream);
sync_check_cuda_error(stream);
}
// do multinomial sampling
{
TopPSamplingKernelParams<T> samplingParams{};
samplingParams.probs = probs;
samplingParams.outputIdsPtrs = outputIdsPtrs;
samplingParams.workspace = samplingWorkspace;
samplingParams.topPs = runtimeMultinomialTopP;
samplingParams.batchSlots = params.batchSlots;
samplingParams.curandState = params.curandStats;
samplingParams.randomVals = params.randomVals;
samplingParams.skipDecode = skipDecodePtr;
samplingParams.batchSize = params.batchSize * params.maxDecodingTokens;
samplingParams.maxBatchSize = params.batchSize * params.maxDecodingTokens;
samplingParams.vocabSizePadded = params.vocabSize;
samplingParams.maxSeqLen = 1;
samplingParams.blockNum
= calcAirTopPBlockNum<T>(samplingParams.batchSize, samplingParams.vocabSizePadded, params.smCnt, true);
samplingParams.isDeterministic = true;
samplingParams.checkParams();
tensorrt_llm::kernels::invokeBatchAirTopPSampling<T>(samplingParams, stream);
sync_check_cuda_error(stream);
}
}
template void typicalAcceptanceSampling(TypicalAcceptanceSampling<float> const& params, cudaStream_t stream);
template void typicalAcceptanceSampling(TypicalAcceptanceSampling<half> const& params, cudaStream_t stream);
template <typename T>
size_t getTypicalAcceptanceWorkspaceSize(SizeType32 batchSize, SizeType32 maxDecodingTokens, SizeType32 vocabSizePadded)
{
SizeType32 constexpr NUM_BUFFERS{6};
size_t workspaces[NUM_BUFFERS];
workspaces[0] = tensorrt_llm::kernels::getAirTopPWorkspaceSize<T>(
batchSize * maxDecodingTokens, vocabSizePadded, /* isDeterministic */ true);
// entropy
workspaces[1] = batchSize * maxDecodingTokens * sizeof(float);
// runtimeMultinomialTopP
workspaces[2] = batchSize * maxDecodingTokens * sizeof(float);
// probs
workspaces[3] = batchSize * maxDecodingTokens * vocabSizePadded * sizeof(T);
// outputIdsPtrs
workspaces[4] = batchSize * maxDecodingTokens * sizeof(TokenIdType*);
// skipDecode
workspaces[5] = batchSize * maxDecodingTokens * sizeof(bool);
auto const workspaceSize = tensorrt_llm::common::calculateTotalWorkspaceSize(workspaces, NUM_BUFFERS);
return workspaceSize;
}
template size_t getTypicalAcceptanceWorkspaceSize<float>(
SizeType32 batchSize, SizeType32 maxDecodingTokens, SizeType32 vocabSizePadded);
template size_t getTypicalAcceptanceWorkspaceSize<half>(
SizeType32 batchSize, SizeType32 maxDecodingTokens, SizeType32 vocabSizePadded);
} // namespace tensorrt_llm::kernels::speculative_decoding