6403c957e0
Issue 6754 reports that Go bzip2 Decode function is much slower (about 2.5x in go1.5) than the Python equivalent (which is actually just a wrapper around the usual C library) on random data. Profiling the code shows that half a dozen of CMP instructions in a tight loop are responsibile for most of the execution time. This patch reduces the number of branches of the loop, greatly improving performance on random data and speeding up decoding of real data. name old time/op new time/op delta DecodeDigits-4 9.28ms ± 1% 8.05ms ± 1% -13.18% (p=0.000 n=15+14) DecodeTwain-4 28.9ms ± 2% 26.4ms ± 1% -8.57% (p=0.000 n=15+14) DecodeRand-4 3.94ms ± 1% 3.06ms ± 1% -22.45% (p=0.000 n=15+14) name old speed new speed delta DecodeDigits-4 4.65MB/s ± 1% 5.36MB/s ± 1% +15.21% (p=0.000 n=13+14) DecodeTwain-4 4.32MB/s ± 2% 4.72MB/s ± 1% +9.36% (p=0.000 n=15+14) DecodeRand-4 4.27MB/s ± 1% 5.51MB/s ± 1% +28.86% (p=0.000 n=15+14) I've run some benchmark comparing Go bzip2 implementation with the usual Linux bzip2 command (which is written in C). On my machine this patch brings go1.5 from ~2.26x to ~1.50x of bzip2 time (on 64MB random data) from ~1.70x to ~1.50x of bzip2 time (on 100MB english text) from ~2.00x to ~1.88x of bzip2 time (on 64MB /dev/zero data) Fixes #6754 Change-Id: I3cb12d2c0c2243c1617edef1edc88f05f91d26d1 Reviewed-on: https://go-review.googlesource.com/13853 Reviewed-by: Nigel Tao <nigeltao@golang.org> |
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