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[Bug libc/12019] memchr overshoots on Alpha


------- Additional Comments From mcree at orcon dot net dot nz  2010-09-23 10:48 -------
RTH's patch certainly fixes the segfault that was in the test case reported by
Debian.  Speed tests also show it runs faster when searching large memory
buffers.  I allocated 100Mbytes memory, filled it with 0xff except for a 0x00
half way in, then timed the memchr() search for the 0x00.  With current memchr()
(alphaev6 optimised version from Debian's libc6.1-alphaev67 package) get (after
averaging over 10 memchr() searches):
 
              cycles:  129525563 (scaled from 50.0%)
        instructions:   50746044 (scaled from 50.0%)
        cache-misses:     837238 (scaled from 50.0%)
        mbox-replays:    4416463 (scaled from 25.0%)

With RTH's new version get (compiled with -O2 -mcpu=ev67):

              cycles:   52405038 (scaled from 50.0%)
        instructions:   62017822 (scaled from 50.0%)
        cache-misses:    1034687 (scaled from 50.0%)
        mbox-replays:       6866 (scaled from 25.0%)

so while it executes more CPU instructions it does it much faster!  It's over
twice as fast as the old version.  Nice.  The almost complete removal of Mbox
replay traps is presumably a significant part of the speedup.


-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=12019

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