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List:       freebsd-hackers
Subject:    Re: speed tests (Re: Replace bcopy() to update ether_addr)
From:       Luigi Rizzo <rizzo () iet ! unipi ! it>
Date:       2012-08-22 14:54:29
Message-ID: 20120822145429.GB64686 () onelab2 ! iet ! unipi ! it
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On Wed, Aug 22, 2012 at 05:26:47PM +0300, Mitya wrote:
> 22.08.2012 17:36, Luigi Rizzo ??????????????:
> >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

i forgot to mention that i tried this only on amd64, my ASM is horrible.
Just comment out the offending lines and do not run those tests.

Or, if you have a portable fix, let me know and everybody will
appreciate it.

cheers
luigi

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