106 lines
4.0 KiB
Diff
106 lines
4.0 KiB
Diff
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# http://mail.madler.net/pipermail/zlib-devel_madler.net/2012-June/002907.html
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# http://mail.madler.net/pipermail/zlib-devel_madler.net/2012-August/002977.html
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From: Andreas Krebbel krebbel at linux.vnet.ibm.com
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Subject: RFC: Improve longest_match performance
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The code currently generated for longest_match looks far from optimal
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due to a bunch of pointless zero/sign extend instructions.
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By just promoting a few data types in the function I was able to get
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rid of all but two. The new hotloop is almost half the size of the
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original version providing quite a performance win for S/390:
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Measured on a zEnterprise z196
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zlib compiled with upstream GCC 4.8 branch
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32 bit old new
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256MB randomdata: 11.65s 10.92s 6.68%
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100MB manpages: 4.23s 4.14s 2.17%
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217MB PDF: 10.54s 9.44s 11.65%
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unaligned ok
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256MB randomdata: 10.90s 10.54s 3.41%
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100MB manpages: 3.94s 3.87s 1.81%
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217MB PDF: 8.77s 8.64s 1.50%
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64 bit old new
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256MB randomdata: 11.90s 11.43s 4.11%
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100MB manpages: 4.51s 4.44s 1.58%
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217MB PDF: 10.11s 9.89s 2.22%
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unaligned ok
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256MB randomdata: 11.51s 11.15s 3.23%
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100MB manpages: 4.33s 3.99s 8.52%
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217MB PDF: 9.81s 9.02s 8.76%
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I also did some measurements on x86 and Power:
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For Power (64 bit, unaligned_ok) an additional zero extend
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appears. However, the impact is not measurable. There are minor wins
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and minor regressions. The overall result is flat.
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For Core2 32 bit the patch is a clear winner with up to 9% for the pdf
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test. Also on 64 bit the code optimized for Core2 gets a bit smaller
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but unfortunately causes some regressions which I cannot explain.
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For mainframe customers the performance of zlib is very important so I
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would be very happy to see the patch integrated into upstream
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zlib. Given that the patch might cause minor regressions on other
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targets, would it be possible to enable it arch-dependent?
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See below for the patch and some code snippets from my tests.
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Bye,
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-Andreas-
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---
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deflate.c | 15 ++++++++-------
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1 file changed, 8 insertions(+), 7 deletions(-)
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Index: zlib-1.2.7/deflate.c
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===================================================================
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--- zlib-1.2.7.orig/deflate.c 2012-02-13 01:15:47.000000000 +0100
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+++ zlib-1.2.7/deflate.c 2012-09-27 13:39:57.942762946 +0200
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@@ -1143,15 +1143,16 @@
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/* For 80x86 and 680x0, an optimized version will be provided in match.asm or
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* match.S. The code will be functionally equivalent.
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*/
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-local uInt longest_match(s, cur_match)
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+local uInt longest_match(s, pcur_match)
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deflate_state *s;
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- IPos cur_match; /* current match */
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+ IPos pcur_match; /* current match */
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{
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+ ptrdiff_t cur_match = pcur_match; /* extend to pointer width */
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unsigned chain_length = s->max_chain_length;/* max hash chain length */
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register Bytef *scan = s->window + s->strstart; /* current string */
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register Bytef *match; /* matched string */
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register int len; /* length of current match */
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- int best_len = s->prev_length; /* best match length so far */
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+ ptrdiff_t best_len = s->prev_length; /* best match length so far */
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int nice_match = s->nice_match; /* stop if match long enough */
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IPos limit = s->strstart > (IPos)MAX_DIST(s) ?
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s->strstart - (IPos)MAX_DIST(s) : NIL;
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@@ -1166,12 +1167,12 @@
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* Try with and without -DUNALIGNED_OK to check.
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*/
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register Bytef *strend = s->window + s->strstart + MAX_MATCH - 1;
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- register ush scan_start = *(ushf*)scan;
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- register ush scan_end = *(ushf*)(scan+best_len-1);
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+ register uInt scan_start = *(ushf*)scan;
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+ register uInt scan_end = *(ushf*)(scan+best_len-1);
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#else
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register Bytef *strend = s->window + s->strstart + MAX_MATCH;
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- register Byte scan_end1 = scan[best_len-1];
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- register Byte scan_end = scan[best_len];
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+ register uInt scan_end1 = scan[best_len-1];
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+ register uInt scan_end = scan[best_len];
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#endif
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/* The code is optimized for HASH_BITS >= 8 and MAX_MATCH-2 multiple of 16.
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