Date: Mon, 07 Jul 2008 16:21:58 -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: <4872A516.4000306@elischer.org> In-Reply-To: <ed91d4a80807071533r5a93d24cpd01b5ec0f3b2c835@mail.gmail.com> References: <4867420D.7090406@gtcomm.net> <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> <48727BA9.6020702@elischer.org> <ed91d4a80807071533r5a93d24cpd01b5ec0f3b2c835@mail.gmail.com>
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Artem Belevich wrote: >> Prefetching when you are waiting for the data isn't a help. > > Agreed. Got to start prefetch around <put your memory latency here>ns > before you actually need the data and move on doing other things that > do not depend on the data you've just started prefetching. > >> 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". > > It does not have to be 'speculative' either. "*Will*" is just a very definite subset of 'speculation' :-) > In this particular case > we have very good idea that we *will* need some data from ethernet > header and, probably, IP and TCP headers as well. We might as well tel > the hardware to start pulling data in without stalling the CPU. Intel > has instructions specifically for this purpose. I assume AMD has them > too. > > --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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