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[SYCL] Fix host-to-host copy during copyback #1692

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Merged
bader merged 2 commits into from
May 16, 2020
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[SYCL] Fix host-to-host copy during copyback #1692

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[SYCL] Fix host-to-host copy during copyback
sergey-semenov May 15, 2020
6461b08
Appease clang-format check
sergey-semenov May 15, 2020
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10 changes: 6 additions & 4 deletions sycl/source/detail/memory_manager.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -358,13 +358,15 @@ static void copyH2H(SYCLMemObjI *SYCLMemObj, char *SrcMem,
PI_INVALID_OPERATION);
}

DstOffset[0] *= DstElemSize;
SrcOffset[0] *= SrcElemSize;
SrcMem += SrcOffset[0] * SrcElemSize;

@s-kanaev s-kanaev May 15, 2020

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Just curious.
Why only SrcOffset[0] is involved? Is multidimensional offset "merged" into singledimensional?

@v-klochkov v-klochkov May 15, 2020

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I think the checks at lines 353-355 in this file make this line 361 correct. If Dim > 1, then the statement is SrcMem += 0;

@v-klochkov v-klochkov May 15, 2020

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Honestly speaking it is hard to believe that std::memcpy() does not check src==dst case and does something wrong in such case.

Why did you decide fixing this, did you really noticed unexpected behavior when src==dst?

@sergey-semenov sergey-semenov May 18, 2020

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@v-klochkov I have indeed encountered such behaviour when linking with Intel's implementation of memcpy (_intel_fast_memcpy).

DstMem += DstOffset[0] * DstElemSize;

if (SrcMem == DstMem)
return;

size_t BytesToCopy =
SrcAccessRange[0] * SrcElemSize * SrcAccessRange[1] * SrcAccessRange[2];

std::memcpy(DstMem + DstOffset[0], SrcMem + SrcOffset[0], BytesToCopy);
std::memcpy(DstMem, SrcMem, BytesToCopy);
}

// Copies memory between: host and device, host and host,
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