Date: Mon, 7 Jul 2008 12:27:52 -0700 From: "Artem Belevich" <fbsdlist@src.cx> To: "FreeBSD Net" <freebsd-net@freebsd.org> Subject: Re: Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp] Message-ID: <ed91d4a80807071227q5d9ca283g59270a1ab92c80a9@mail.gmail.com> In-Reply-To: <20080708045135.V1022@besplex.bde.org> 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>
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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. Just my $0.02. --Artem
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