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#ifndef CAFFE2_UTILS_GPU_BITONIC_SORT_H_
#define CAFFE2_UTILS_GPU_BITONIC_SORT_H_
#include "caffe2/utils/math.h"
#include "caffe2/utils/GpuDefs.cuh"
namespace caffe2 {
// Returns true if the given integer type is a power-of-2 (positive only)
// Note(jiayq): windows reported an error per
// https://github.com/caffe2/caffe2/issues/997
// and as a result will make it a macro.
#ifdef _MSC_VER
#define integerIsPowerOf2(v) ((v) && !((v) & ((v) - 1)))
#else // _MSC_VER
template <typename T>
constexpr bool integerIsPowerOf2(T v) {
return (v && !(v & (v - 1)));
}
#endif // _MSC_VER
/// The maximum in-block bitonic sort we support
constexpr int kMaxBitonicSortSize = 4096;
template <typename T>
__device__ inline void swapVars(T& t1, T& t2) {
T tmp = t1;
t1 = t2;
t2 = tmp;
}
template <typename Comparator, typename K, typename V>
__device__ inline void bitonicSwap(K& kA, V& vA,
K& kB, V& vB,
bool dir,
const Comparator& comp) {
bool swap = comp(kA, vA, kB, vB);
if (swap == dir) {
swapVars(kA, kB);
swapVars(vA, vB);
}
};
template <typename Comparator, typename K, typename V,
int Power2SortSize,
int ThreadsPerBlock>
__device__ inline void bitonicSort(K* keys,
V* values,
const Comparator& comp) {
static_assert(Power2SortSize <= kMaxBitonicSortSize,
"sort size <= 4096 only supported");
// Assume the sort is taking place in shared memory
// static_assert(Power2SortSize * (sizeof(K) + sizeof(V)) < 32768,
// "sort data too large (>32768 bytes)");
static_assert(integerIsPowerOf2(Power2SortSize),
"sort size must be power of 2");
static_assert(integerIsPowerOf2(ThreadsPerBlock),
"threads in block must be power of 2");
// If what we are sorting is too small, then not all threads
// participate
constexpr int numThreadsForSort = Power2SortSize / 2;
constexpr bool allThreads = numThreadsForSort >= ThreadsPerBlock;
// If what we are sorting is too large, then threads must loop more
// than once
constexpr int loopPerThread =
allThreads ? numThreadsForSort / ThreadsPerBlock : 1;
#pragma unroll
for (int size = 2; size < Power2SortSize; size *= 2) {
#pragma unroll
for (int stride = size / 2; stride > 0; stride /= 2) {
#pragma unroll
for (int loop = 0; loop < loopPerThread; ++loop) {
int threadId = loop * ThreadsPerBlock + threadIdx.x;
bool flag = ((threadId & (size / 2)) != 0);
int pos = 2 * threadId - (threadId & (stride - 1));
if (allThreads || (threadId < numThreadsForSort)) {
bitonicSwap<Comparator, K, V>(
keys[pos], values[pos],
keys[pos + stride], values[pos + stride],
flag, comp);
}
__syncthreads();
}
}
}
#pragma unroll
for (int stride = Power2SortSize / 2; stride > 0; stride /= 2) {
#pragma unroll
for (int loop = 0; loop < loopPerThread; ++loop) {
int threadId = loop * ThreadsPerBlock + threadIdx.x;
int pos = 2 * threadId - (threadId & (stride - 1));
if (allThreads || (threadId < numThreadsForSort)) {
bitonicSwap<Comparator, K, V>(
keys[pos], values[pos],
keys[pos + stride], values[pos + stride],
false, comp);
}
__syncthreads();
}
}
}
template <typename Comparator, typename K, typename V, int Power2SortSize>
__device__ inline void warpBitonicSort(K* keys,
V* values,
const Comparator& comp) {
// Smaller sorts should use a warp shuffle sort
static_assert(Power2SortSize > kWarpSize,
"sort not large enough");
static_assert(integerIsPowerOf2(Power2SortSize),
"sort size must be power of 2");
static_assert(Power2SortSize <= kMaxBitonicSortSize,
"sort size <= 4096 only supported");
// If what we are sorting is too large, then lanes must loop more
// than once
constexpr int loopPerThread = (Power2SortSize / 2) / kWarpSize;
int laneId = getLaneId();
#pragma unroll
for (int size = 2; size < Power2SortSize; size *= 2) {
#pragma unroll
for (int stride = size / 2; stride > 0; stride /= 2) {
#pragma unroll
for (int loop = 0; loop < loopPerThread; ++loop) {
int threadId = loop * kWarpSize + laneId;
bool flag = ((threadId & (size / 2)) != 0);
int pos = 2 * threadId - (threadId & (stride - 1));
bitonicSwap<Comparator, K, V>(
keys[pos], values[pos],
keys[pos + stride], values[pos + stride],
flag, comp);
__threadfence_block();
}
}
}
#pragma unroll
for (int stride = Power2SortSize / 2; stride > 0; stride /= 2) {
#pragma unroll
for (int loop = 0; loop < loopPerThread; ++loop) {
int threadId = loop * kWarpSize + laneId;
int pos = 2 * threadId - (threadId & (stride - 1));
bitonicSwap<Comparator, K, V>(
keys[pos], values[pos],
keys[pos + stride], values[pos + stride],
false, comp);
__threadfence_block();
}
}
}
} // namespace caffe2
#endif // CAFFE2_UTILS_GPU_BITONIC_SORT_H_
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