Date: Thu, 3 May 2012 11:49:38 +0100 From: Attilio Rao <attilio@freebsd.org> To: Steven Atreju <snatreju@googlemail.com> Cc: net@freebsd.org, Luigi Rizzo <rizzo@iet.unipi.it>, "K. Macy" <kmacy@freebsd.org>, current@freebsd.org Subject: Re: fast bcopy... Message-ID: <CAJ-FndDFg3eGHfiGtPSHgc06dFPB7VUZAq1moZxZBy=6n_rNRA@mail.gmail.com> In-Reply-To: <20120503102844.GU633@sherwood.local> References: <20120502182557.GA93838@onelab2.iet.unipi.it> <20120502215249.GT633@sherwood.local> <CAHM0Q_NNoMrtwcz-xoQ34oVmgJSyjeb_7O6qBHCe16eFeTot_w@mail.gmail.com> <20120503102844.GU633@sherwood.local>
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2012/5/3, Steven Atreju <snatreju@googlemail.com>: > K. Macy wrote [2012-05-03 02:58+0200]: >> It's highly chipset and processor dependent what works best. > > Yes, of course. > Though i was kinda, even shocked, once i've seen this first: > > http://marc.info/?l=dragonfly-commits&m=132241713812022&w=2 > > So we don't use our assembler version for new gccs and HAMMER or > SSE3+ (the decision for these was rather arbitrarily, except they > were yet existent for an instant implementation). > >> Intel now has non-temporal loads and stores which work much >> better in some cases but provide little benefit in others. > > Yes, our 2002 tests have shown that these were *extremely* > dependent upon alignment. (Note: 2002. o-) > Hmm, it doesn't really matter, but i guess this is a good time to > thank the FreeBSD hackers for that FPU stack FILD/FISTP idea! > I'll append the copy related notes of our doc/memperf.txt. > Thanks, I made an implementation of fpu unwinding and mmx copy to see if they were really making a difference years ago (reimplementing bcopy, memcopy, etc.). What really mattered with hw available at that time (pentium4) was the alignment and use of non-temporal operations on heavilly contended cache-lines. In few words it is more important we engineer the "buffer" layout rather than the functions themselves. Attilio -- Peace can only be achieved by understanding - A. Einstein
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