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swap axis for optimization in Tensor3dCopy() #1

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merged 1 commit into from
Oct 26, 2015
Merged

swap axis for optimization in Tensor3dCopy() #1

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44 changes: 42 additions & 2 deletions src/ctc/cctc-tombstone.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -24,11 +24,50 @@
namespace kaldi {
namespace ctc {

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There should be a comment here briefly explaining what the does; and since this function is not exported, it's good practice to declare it 'static'.

// This function is used inside Tensor3dCopy to swap x with y(or z) if x's
// stride is not 1 but y(or z)'s stride is 1. Since x maps to the thread
// index in GPU, it would be more efficient if {src|dest}_xstride is 1.
// Note that the one with both src and dst strides being 1 is more preferable
// to swap with x than those with only src or dst stride being 1.
static void SwapDimsForX(int32* xdim, int32* ydim, int32* zdim,
int32* src_xstride, int32* src_ystride, int32* src_zstride,
int32* dst_xstride, int32* dst_ystride, int32* dst_zstride) {
if (*src_xstride != 1 || *dst_xstride != 1) {
// first try to look for y or z with both src and dst strides being 1
if (*src_ystride == 1 && *dst_ystride == 1) {
std::swap(*xdim, *ydim);
std::swap(*src_xstride, *src_ystride);
std::swap(*dst_xstride, *dst_ystride);
}
else if (*src_zstride == 1 && *dst_zstride == 1) {
std::swap(*xdim, *zdim);
std::swap(*src_xstride, *src_zstride);
std::swap(*dst_xstride, *dst_zstride);
}
// then try to look for the one with only src or dst stride being 1
else if (*src_xstride != 1 && *dst_xstride != 1) {
if (*src_ystride == 1 || *dst_ystride == 1) {
std::swap(*xdim, *ydim);
std::swap(*src_xstride, *src_ystride);
std::swap(*dst_xstride, *dst_ystride);
}
else if (*src_zstride == 1 || *dst_zstride == 1) {
std::swap(*xdim, *zdim);
std::swap(*src_xstride, *src_zstride);
std::swap(*dst_xstride, *dst_zstride);
}
}
}
}

template <typename Real>
void Tensor3dCopy(int32 xdim, int32 ydim, int32 zdim,
int32 src_xstride, int32 src_ystride, int32 src_zstride,
int32 dst_xstride, int32 dst_ystride, int32 dst_zstride,
const Real *src, Real *dst) {
SwapDimsForX(&xdim, &ydim, &zdim, &src_xstride, &src_ystride, &src_zstride,
&dst_xstride, &dst_ystride, &dst_zstride);

#if HAVE_CUDA == 1
if (CuDevice::Instantiate().Enabled()) {
Timer tim;
Expand All @@ -45,9 +84,10 @@ void Tensor3dCopy(int32 xdim, int32 ydim, int32 zdim,
} else
#endif
{
for (int32 x = 0; x < xdim; x++)
// iterate over z, y, x if xstride is 1, for memory-locality reasons.
for (int32 z = 0; z < zdim; z++)
for (int32 y = 0; y < ydim; y++)
for (int32 z = 0; z < zdim; z++)
for (int32 x = 0; x < xdim; x++)
dst[x * dst_xstride + y * dst_ystride + z * dst_zstride] =
src[x * src_xstride + y * src_ystride + z * src_zstride];
}
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