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Re-work fast path that emits copies in zippy compression.

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The primary motivation for the change is that FindMatchLength is
likely to discover a difference in the first 8 bytes it compares.
If that occurs then we know the length of the match is less than 12,
because FindMatchLength is invoked after a 4-byte match is found.
When emitting a copy, it is useful to know that the length is less
than 12 because the two-byte variant of an emitted copy requires that.

This is a performance-tuning change that should not affect the
library's behavior.

With FDO on perflab/Haswell the geometric mean for ZFlat/* went from
47,290ns to 45,741ns, an improvement of 3.4%.

SAMPLE (before)

BM_ZFlat/0      102824     102650      40691 951.4MB/s  html (22.31 %)
BM_ZFlat/1     1293512    1290442       3225 518.9MB/s  urls (47.78 %)
BM_ZFlat/2       10373      10353     417959 11.1GB/s  jpg (99.95 %)
BM_ZFlat/3         268        268   15745324 712.4MB/s  jpg_200 (73.00 %)
BM_ZFlat/4       12137      12113     342462 7.9GB/s  pdf (83.30 %)
BM_ZFlat/5      430672     429720       9724 909.0MB/s  html4 (22.52 %)
BM_ZFlat/6      420541     419636       9833 345.6MB/s  txt1 (57.88 %)
BM_ZFlat/7      373829     373158      10000 319.9MB/s  txt2 (61.91 %)
BM_ZFlat/8     1119014    1116604       3755 364.5MB/s  txt3 (54.99 %)
BM_ZFlat/9     1544203    1540657       2748 298.3MB/s  txt4 (66.26 %)
BM_ZFlat/10      91041      90866      46002 1.2GB/s  pb (19.68 %)
BM_ZFlat/11     332766     331990      10000 529.5MB/s  gaviota (37.72 %)
BM_ZFlat/12      39960      39886     100000 588.3MB/s  cp (48.12 %)
BM_ZFlat/13      14493      14465     287181 735.1MB/s  c (42.47 %)
BM_ZFlat/14       4447       4440     947927 799.3MB/s  lsp (48.37 %)
BM_ZFlat/15    1316362    1313350       3196 747.7MB/s  xls (41.23 %)
BM_ZFlat/16        312        311   10000000 613.0MB/s  xls_200 (78.00 %)
BM_ZFlat/17     388471     387502      10000 1.2GB/s  bin (18.11 %)
BM_ZFlat/18         65         64   64838208 2.9GB/s  bin_200 (7.50 %)
BM_ZFlat/19      65900      65787      63099 554.3MB/s  sum (48.96 %)
BM_ZFlat/20       6188       6177     681951 652.6MB/s  man (59.21 %)

SAMPLE (after)

Benchmark     Time(ns)    CPU(ns) Iterations
--------------------------------------------
BM_ZFlat/0       99259      99044      42428 986.0MB/s  html (22.31 %)
BM_ZFlat/1     1257039    1255276       3341 533.4MB/s  urls (47.78 %)
BM_ZFlat/2       10044      10030     405781 11.4GB/s  jpg (99.95 %)
BM_ZFlat/3         268        267   15732282 713.3MB/s  jpg_200 (73.00 %)
BM_ZFlat/4       11675      11657     358629 8.2GB/s  pdf (83.30 %)
BM_ZFlat/5      420951     419818       9739 930.5MB/s  html4 (22.52 %)
BM_ZFlat/6      415460     414632      10000 349.8MB/s  txt1 (57.88 %)
BM_ZFlat/7      367191     366436      10000 325.8MB/s  txt2 (61.91 %)
BM_ZFlat/8     1098345    1096036       3819 371.3MB/s  txt3 (54.99 %)
BM_ZFlat/9     1508701    1505306       2758 305.3MB/s  txt4 (66.26 %)
BM_ZFlat/10      87195      87031      47289 1.3GB/s  pb (19.68 %)
BM_ZFlat/11     322338     321637      10000 546.5MB/s  gaviota (37.72 %)
BM_ZFlat/12      36739      36668     100000 639.9MB/s  cp (48.12 %)
BM_ZFlat/13      13646      13618     304009 780.9MB/s  c (42.47 %)
BM_ZFlat/14       4249       4240     992456 837.0MB/s  lsp (48.37 %)
BM_ZFlat/15    1262925    1260012       3314 779.4MB/s  xls (41.23 %)
BM_ZFlat/16        308        308   10000000 619.8MB/s  xls_200 (78.00 %)
BM_ZFlat/17     379750     378944      10000 1.3GB/s  bin (18.11 %)
BM_ZFlat/18         62         62   67443280 3.0GB/s  bin_200 (7.50 %)
BM_ZFlat/19      61706      61587      67645 592.1MB/s  sum (48.96 %)
BM_ZFlat/20       5968       5958     698974 676.6MB/s  man (59.21 %)
This commit is contained in:
Geoff Pike
2016-06-28 11:53:11 -07:00
committed by Alkis Evlogimenos
parent 094c67de88
commit 38a5ec5fca
3 changed files with 76 additions and 49 deletions
Download Patch File Download Diff File Expand all files Collapse all files

7
snappy_unittest.cc
View File

@@ -1054,7 +1054,9 @@ TEST(Snappy, ZeroOffsetCopyValidation) {
namespace {
int TestFindMatchLength(const char* s1, const char *s2, unsigned length) {
return snappy::internal::FindMatchLength(s1, s2, s2 + length);
pair<size_t, bool> p = snappy::internal::FindMatchLength(s1, s2, s2 + length);
CHECK_EQ(p.first < 8, p.second);
return p.first;
}
} // namespace
@@ -1164,8 +1166,7 @@ TEST(Snappy, FindMatchLengthRandom) {
}
DataEndingAtUnreadablePage u(s);
DataEndingAtUnreadablePage v(t);
int matched = snappy::internal::FindMatchLength(
u.data(), v.data(), v.data() + t.size());
int matched = TestFindMatchLength(u.data(), v.data(), t.size());
if (matched == t.size()) {
EXPECT_EQ(s, t);
} else {