Date: Wed, 22 Aug 2012 17:26:47 +0300 From: Mitya <mitya@cabletv.dp.ua> To: Luigi Rizzo <rizzo@iet.unipi.it>, freebsd-net@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: speed tests (Re: Replace bcopy() to update ether_addr) Message-ID: <5034EC27.1070203@cabletv.dp.ua> In-Reply-To: <20120822143632.GA64686@onelab2.iet.unipi.it> References: <20120821112415.GA50078@onelab2.iet.unipi.it> <201208220232.q7M2WLCL020204@ref10-i386.freebsd.org> <20120822143632.GA64686@onelab2.iet.unipi.it>
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22.08.2012 17:36, Luigi Rizzo написал: > On Wed, Aug 22, 2012 at 02:32:21AM +0000, Bruce Evans wrote: >> luigi wrote: >> >>> even more orthogonal: >>> >>> I found that copying 8n + (5, 6 or 7) bytes was much much slower than >>> copying a multiple of 8 bytes. For n=0, 1,2,4,8 bytes are efficient, >>> other cases are slow (turned into 2 or 3 different writes). >>> >>> The netmap code uses a pkt_copy routine that does exactly this >>> rounding, gaining some 10-20ns per packet for small sizes. >> I don't believe 10-20ns for just the extra bytes. memcpy() ends up >> with a movsb to copy the extra bytes. This can be slow, but I don't >> believe 10-20ns (except on machines running at i486 speeds of course). > I am adding at the end a test program so people can try things on their hw. > > Build it with > > cc -O2 -Werror -Wall -Wextra -lpthread -lrt testlock.c -o testlock > > # uname -a FreeBSD m18.cabletv.dp.ua 9.0-STABLE FreeBSD 9.0-STABLE #1: Tue Apr 24 13:23:05 EEST 2012 root@m18.cabletv.dp.ua:/usr/src/sys/i386/compile/m18 i386 cc -O2 -Werror -Wall -Wextra -lpthread -lrt testlock.c -o testlock testlock.c: In function 'test_rdtsc': testlock.c:151: error: can't find a register in class 'AD_REGS' while reloading 'asm' testlock.c:151: error: 'asm' operand has impossible constraints
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