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Re: [PATCH 2/2] Improve 64bit memcpy/memmove for Corei7 with avx2 instruction
- From: OndÅej BÃlka <neleai at seznam dot cz>
- To: Ling Ma <ling dot ma dot program at gmail dot com>
- Cc: Nix <nix at esperi dot org dot uk>, libc-alpha at sourceware dot org, hongjiu dot lu at intel dot com
- Date: Fri, 7 Jun 2013 20:02:22 +0200
- Subject: Re: [PATCH 2/2] Improve 64bit memcpy/memmove for Corei7 with avx2 instruction
- References: <20130605121816 dot GA11269 at domone dot kolej dot mff dot cuni dot cz> <CAOGi=dMiD=_Qf1EJ=F3hfyQDtQubDEC5pjpXKDCHrUQwhr=vzg at mail dot gmail dot com> <20130605161954 dot GA26401 at domone dot kolej dot mff dot cuni dot cz> <CAOGi=dPWPaX5prcL-uAaqS6=_ehzKeBmAFMdwV6aU34jZ0eHtQ at mail dot gmail dot com> <20130606125511 dot GA28565 at domone dot kolej dot mff dot cuni dot cz> <CAOGi=dPs9geCtrWhU1L_0DEfOWOknpzFSLmYs4gbYzGX8Zn5Hg at mail dot gmail dot com> <20130607104613 dot GA6343 at domone dot kolej dot mff dot cuni dot cz> <8761xqru5w dot fsf at spindle dot srvr dot nix> <CAOGi=dMV5jaS2597cksd0mW84UDd06SovsBkL5=WPez-jZWg4g at mail dot gmail dot com> <CAOGi=dPfR2OHg+OkD0hXS2sDFQRcTUqhrjrrdyymwsxPfeNcRQ at mail dot gmail dot com>
On Fri, Jun 07, 2013 at 09:51:38PM +0800, Ling Ma wrote:
> Hi Ondra,
> If we prefer to backward copy, it will cause memory false dpendence
> and impact our performance as we mentioned above.
>
I tried it on for sse and results of bacward copy are only about 10
in worst case cycles slower. It may be also explained that computation
of bounds is more complicated but effect of false memory dependence is
minimal.