Date: Mon, 07 Jul 2008 13:25:13 -0700 From: Julian Elischer <julian@elischer.org> To: Artem Belevich <fbsdlist@src.cx> Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp] Message-ID: <48727BA9.6020702@elischer.org> In-Reply-To: <ed91d4a80807071227q5d9ca283g59270a1ab92c80a9@mail.gmail.com> References: <4867420D.7090406@gtcomm.net> <alpine.LFD.1.10.0807052356130.2145@filebunker.xip.at> <2d3001c8def1$f4309b90$020b000a@bartwrkstxp> <486FFF70.3090402@gtcomm.net> <48701921.7090107@gtcomm.net> <4871E618.1080500@freebsd.org> <20080708002228.G680@besplex.bde.org> <48724238.2020103@freebsd.org> <20080708034304.R21502@delplex.bde.org> <20080708045135.V1022@besplex.bde.org> <ed91d4a80807071227q5d9ca283g59270a1ab92c80a9@mail.gmail.com>
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Artem Belevich wrote: > Hi, > > As was already mentioned, we can't avoid all cache misses as there's > data that's recently been updated in memory via DMA and therefor > kicked out of cache. > > However, we may hide some of the latency penalty by prefetching > 'interesting' data early. I.e. we know that we want to access some > ethernet headers, so we may start pulling relevant data into cache > early. Ideally, by the time we need to access the field, it will > already be in the cache. When we're counting nanoseconds per packet > this may bring some performance gain. Prefetching when you are waiting for the data isn't a help. what you need is a speculative prefetch where you an tell teh processor "We will probably need the following address so start getting it while we go do other stuff". As far as I know we have no capacity to do that.. > > Just my $0.02. > --Artem > _______________________________________________ > freebsd-net@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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