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IVFUtilsSelect1.cu
/**
* Copyright (c) 2015-present, Facebook, Inc.
* All rights reserved.
*
* This source code is licensed under the BSD+Patents license found in the
* LICENSE file in the root directory of this source tree.
*/
// Copyright 2004-present Facebook. All Rights Reserved.
#include "IVFUtils.cuh"
#include "../utils/DeviceUtils.h"
#include "../utils/Limits.cuh"
#include "../utils/Select.cuh"
#include "../utils/StaticUtils.h"
#include "../utils/Tensor.cuh"
//
// This kernel is split into a separate compilation unit to cut down
// on compile time
//
namespace faiss { namespace gpu {
template <int ThreadsPerBlock, int NumWarpQ, int NumThreadQ, bool Dir>
__global__ void
pass1SelectLists(Tensor<int, 2, true> prefixSumOffsets,
Tensor<float, 1, true> distance,
int nprobe,
int k,
Tensor<float, 3, true> heapDistances,
Tensor<int, 3, true> heapIndices) {
constexpr int kNumWarps = ThreadsPerBlock / kWarpSize;
__shared__ float smemK[kNumWarps * NumWarpQ];
__shared__ int smemV[kNumWarps * NumWarpQ];
constexpr auto kInit = Dir ? kFloatMin : kFloatMax;
BlockSelect<float, int, Dir, Comparator<float>,
NumWarpQ, NumThreadQ, ThreadsPerBlock>
heap(kInit, -1, smemK, smemV, k);
auto queryId = blockIdx.y;
auto sliceId = blockIdx.x;
auto numSlices = gridDim.x;
int sliceSize = (nprobe / numSlices);
int sliceStart = sliceSize * sliceId;
int sliceEnd = sliceId == (numSlices - 1) ? nprobe :
sliceStart + sliceSize;
auto offsets = prefixSumOffsets[queryId].data();
// We ensure that before the array (at offset -1), there is a 0 value
int start = *(&offsets[sliceStart] - 1);
int end = offsets[sliceEnd - 1];
int num = end - start;
int limit = utils::roundDown(num, kWarpSize);
int i = threadIdx.x;
auto distanceStart = distance[start].data();
// BlockSelect add cannot be used in a warp divergent circumstance; we
// handle the remainder warp below
for (; i < limit; i += blockDim.x) {
heap.add(distanceStart[i], start + i);
}
// Handle warp divergence separately
if (i < num) {
heap.addThreadQ(distanceStart[i], start + i);
}
// Merge all final results
heap.reduce();
// Write out the final k-selected values; they should be all
// together
for (int i = threadIdx.x; i < k; i += blockDim.x) {
heapDistances[queryId][sliceId][i] = smemK[i];
heapIndices[queryId][sliceId][i] = smemV[i];
}
}
void
runPass1SelectLists(Tensor<int, 2, true>& prefixSumOffsets,
Tensor<float, 1, true>& distance,
int nprobe,
int k,
bool chooseLargest,
Tensor<float, 3, true>& heapDistances,
Tensor<int, 3, true>& heapIndices,
cudaStream_t stream) {
constexpr auto kThreadsPerBlock = 128;
auto grid = dim3(heapDistances.getSize(1), prefixSumOffsets.getSize(0));
auto block = dim3(kThreadsPerBlock);
#define RUN_PASS(NUM_WARP_Q, NUM_THREAD_Q, DIR) \
do { \
pass1SelectLists<kThreadsPerBlock, NUM_WARP_Q, NUM_THREAD_Q, DIR> \
<<<grid, block, 0, stream>>>(prefixSumOffsets, \
distance, \
nprobe, \
k, \
heapDistances, \
heapIndices); \
CUDA_TEST_ERROR(); \
return; /* success */ \
} while (0)
#define RUN_PASS_DIR(DIR) \
do { \
if (k == 1) { \
RUN_PASS(1, 1, DIR); \
} else if (k <= 32) { \
RUN_PASS(32, 2, DIR); \
} else if (k <= 64) { \
RUN_PASS(64, 3, DIR); \
} else if (k <= 128) { \
RUN_PASS(128, 3, DIR); \
} else if (k <= 256) { \
RUN_PASS(256, 4, DIR); \
} else if (k <= 512) { \
RUN_PASS(512, 8, DIR); \
} else if (k <= 1024) { \
RUN_PASS(1024, 8, DIR); \
} \
} while (0)
if (chooseLargest) {
RUN_PASS_DIR(true);
} else {
RUN_PASS_DIR(false);
}
// unimplemented / too many resources
FAISS_ASSERT_FMT(false, "unimplemented k value (%d)", k);
#undef RUN_PASS_DIR
#undef RUN_PASS
}
} } // namespace