Looking up into and decoding the values from char_table has long shown up as a
hotspot in the decompressor. While it turns out that it's hard to make a more
efficient decoder for the copy ops, the literals are simple enough that we can
decode them without needing a table lookup. (This means that 1/4 of the table
is now unused, although that in itself doesn't buy us anything.)
The gains are small, but definitely present; some tests win as much as 10%,
but 1-4% is more typical. These results are from Core i7, in 64-bit mode;
Core 2 and Opteron show similar results. (I've run with more iterations
than unusual to make sure the smaller gains don't drown entirely in noise.)
Benchmark Time(ns) CPU(ns) Iterations
---------------------------------------------------
BM_UFlat/0 74665 74428 182055 1.3GB/s html [ +3.1%]
BM_UFlat/1 714106 711997 19663 940.4MB/s urls [ +4.4%]
BM_UFlat/2 9820 9789 1427115 12.1GB/s jpg [ -1.2%]
BM_UFlat/3 30461 30380 465116 2.9GB/s pdf [ +0.8%]
BM_UFlat/4 301445 300568 46512 1.3GB/s html4 [ +2.2%]
BM_UFlat/5 29338 29263 479452 801.8MB/s cp [ +1.6%]
BM_UFlat/6 13004 12970 1000000 819.9MB/s c [ +2.1%]
BM_UFlat/7 4180 4168 3349282 851.4MB/s lsp [ +1.3%]
BM_UFlat/8 1026149 1024000 10000 959.0MB/s xls [+10.7%]
BM_UFlat/9 237441 236830 59072 612.4MB/s txt1 [ +0.3%]
BM_UFlat/10 203966 203298 69307 587.2MB/s txt2 [ +0.8%]
BM_UFlat/11 627230 625000 22400 651.2MB/s txt3 [ +0.7%]
BM_UFlat/12 836188 833979 16787 551.0MB/s txt4 [ +1.3%]
BM_UFlat/13 351904 350750 39886 1.4GB/s bin [ +3.8%]
BM_UFlat/14 45685 45562 308370 800.4MB/s sum [ +5.9%]
BM_UFlat/15 5286 5270 2656546 764.9MB/s man [ +1.5%]
BM_UFlat/16 78774 78544 178117 1.4GB/s pb [ +4.3%]
BM_UFlat/17 242270 241345 58091 728.3MB/s gaviota [ +1.2%]
BM_UValidate/0 42149 42000 333333 2.3GB/s html [ -3.0%]
BM_UValidate/1 432741 431303 32483 1.5GB/s urls [ +7.8%]
BM_UValidate/2 198 197 71428571 600.7GB/s jpg [+16.8%]
BM_UValidate/3 14560 14521 965517 6.1GB/s pdf [ -4.1%]
BM_UValidate/4 169065 168671 83832 2.3GB/s html4 [ -2.9%]
R=jeff
Revision created by MOE tool push_codebase.
git-svn-id: https://snappy.googlecode.com/svn/trunk@41 03e5f5b5-db94-4691-08a0-1a8bf15f6143
state of ip_ after decompression (or attempted decompresion) is
completely irrelevant, so we don't need the trailer.
Performance is, as expected, mostly flat -- there's a curious ~3-5%
loss in the "lsp" test, but that test case is so short it is hard to say
anything definitive about why (most likely, it's some sort of
unrelated effect).
R=jeff
git-svn-id: https://snappy.googlecode.com/svn/trunk@39 03e5f5b5-db94-4691-08a0-1a8bf15f6143
It is seemingly hard for the compiler to understand that ip_, the current input
pointer into the compressed data stream, can not alias on anything else, and
thus using it directly will incur memory traffic as it cannot be kept in a
register. The code already knew about this and cached it into a local
variable, but since Step() only decoded one tag, it had to move ip_ back into
place between every tag. This seems to have cost us a significant amount of
performance, so changing Step() into a function that decodes as much as it can
before it saves ip_ back and returns. (Note that Step() was already inlined,
so it is not the manual inlining that buys the performance here.)
The wins are about 3-6% for Core 2, 6-13% on Core i7 and 5-12% on Opteron
(for plain array-to-array decompression, in 64-bit opt mode).
There is a tiny difference in the behavior here; if an invalid literal is
encountered (ie., the writer refuses the Append() operation), ip_ will now
point to the byte past the tag byte, instead of where the literal was
originally thought to end. However, we don't use ip_ for anything after
DecompressAllTags() has returned, so this should not change external behavior
in any way.
Microbenchmark results for Core i7, 64-bit (Opteron results are similar):
Benchmark Time(ns) CPU(ns) Iterations
---------------------------------------------------
BM_UFlat/0 79134 79110 8835 1.2GB/s html [ +6.2%]
BM_UFlat/1 786126 786096 891 851.8MB/s urls [+10.0%]
BM_UFlat/2 9948 9948 69125 11.9GB/s jpg [ -1.3%]
BM_UFlat/3 31999 31998 21898 2.7GB/s pdf [ +6.5%]
BM_UFlat/4 318909 318829 2204 1.2GB/s html4 [ +6.5%]
BM_UFlat/5 31384 31390 22363 747.5MB/s cp [ +9.2%]
BM_UFlat/6 14037 14034 49858 757.7MB/s c [+10.6%]
BM_UFlat/7 4612 4612 151395 769.5MB/s lsp [ +9.5%]
BM_UFlat/8 1203174 1203007 582 816.3MB/s xls [+19.3%]
BM_UFlat/9 253869 253955 2757 571.1MB/s txt1 [+11.4%]
BM_UFlat/10 219292 219290 3194 544.4MB/s txt2 [+12.1%]
BM_UFlat/11 672135 672131 1000 605.5MB/s txt3 [+11.2%]
BM_UFlat/12 902512 902492 776 509.2MB/s txt4 [+12.5%]
BM_UFlat/13 372110 371998 1881 1.3GB/s bin [ +5.8%]
BM_UFlat/14 50407 50407 10000 723.5MB/s sum [+13.5%]
BM_UFlat/15 5699 5701 100000 707.2MB/s man [+12.4%]
BM_UFlat/16 83448 83424 8383 1.3GB/s pb [ +5.7%]
BM_UFlat/17 256958 256963 2723 684.1MB/s gaviota [ +7.9%]
BM_UValidate/0 42795 42796 16351 2.2GB/s html [+25.8%]
BM_UValidate/1 490672 490622 1427 1.3GB/s urls [+22.7%]
BM_UValidate/2 237 237 2950297 499.0GB/s jpg [+24.9%]
BM_UValidate/3 14610 14611 47901 6.0GB/s pdf [+26.8%]
BM_UValidate/4 171973 171990 4071 2.2GB/s html4 [+25.7%]
git-svn-id: https://snappy.googlecode.com/svn/trunk@38 03e5f5b5-db94-4691-08a0-1a8bf15f6143
Replace the Apache 2.0 license header by the BSD-type license header;
somehow a lot of the files were missed in the last round.
R=dannyb,csilvers
DELTA=147 (74 added, 2 deleted, 71 changed)
Change on 2011-03-25 19:25:07-07:00 by sesse
Unbreak the build; the relicensing removed a bit too much (only comments
were intended, but I also accidentially removed some of the top lines of
the actual source).
Revision created by MOE tool push_codebase.
MOE_MIGRATION=1072
git-svn-id: https://snappy.googlecode.com/svn/trunk@21 03e5f5b5-db94-4691-08a0-1a8bf15f6143
