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fix benchmark issue when measuring only decoding speed

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zstd bench module can focus on decompression speed _only_.
This is useful when trying to measure performance
on large input data compressed using a high level
as compression time becomes problematic (too long).

This mode is triggered by command : zstd -b -d

Problem was : in such a mode,
measured decoding speed was > 10% slower
than in nominal mode (compression + decompression),
making decompression benchmark mode much less useful.

This patch fixes the issue.
It's not completely clear why, but
moving the `memcpy()` operation sooner in the pipeline fixed it.

I can still measure some difference, but it is in the < 2% range,
so it's much more tolerable.

also : it doesn't matter anymore in which order are selected
commands `-b` and `-d`.
The combination always triggers bench_decodeOnly mode.
This commit is contained in:
Yann Collet 2018-03-05 13:50:07 -08:00
parent 99afe72576
commit 03e7e14192
2 changed files with 8 additions and 5 deletions
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10
programs/bench.c
View File

@ -260,7 +260,11 @@ static int BMK_benchMem(const void* srcBuffer, size_t srcSize,
} } }
/* warmimg up memory */
RDG_genBuffer(compressedBuffer, maxCompressedSize, 0.10, 0.50, 1);
if (g_decodeOnly) {
memcpy(compressedBuffer, srcBuffer, loadedCompressedSize);
} else {
RDG_genBuffer(compressedBuffer, maxCompressedSize, 0.10, 0.50, 1);
}
/* Bench */
{ U64 fastestC = (U64)(-1LL), fastestD = (U64)(-1LL);
@ -373,9 +377,7 @@ static int BMK_benchMem(const void* srcBuffer, size_t srcSize,
ratioAccuracy, ratio,
cSpeedAccuracy, compressionSpeed );
}
} else { /* g_decodeOnly */
memcpy(compressedBuffer, srcBuffer, loadedCompressedSize);
}
} /* if (!g_decodeOnly) */
#if 0 /* disable decompression test */
dCompleted=1;

3
programs/zstdcli.c
View File

@ -573,7 +573,8 @@ int main(int argCount, const char* argv[])
/* Decoding */
case 'd':
#ifndef ZSTD_NOBENCH
if (operation==zom_bench) { BMK_setDecodeOnlyMode(1); argument++; break; } /* benchmark decode (hidden option) */
BMK_setDecodeOnlyMode(1);
if (operation==zom_bench) { argument++; break; } /* benchmark decode (hidden option) */
#endif
operation=zom_decompress; argument++; break;