Date: Mon, 7 Jul 2008 22:56:19 +1000 (EST) From: Bruce Evans <brde@optusnet.com.au> To: Robert Watson <rwatson@FreeBSD.org> Cc: FreeBSD Net <freebsd-net@FreeBSD.org>, Andre Oppermann <andre@FreeBSD.org>, Ingo Flaschberger <if@xip.at>, Paul <paul@gtcomm.net> Subject: Re: Freebsd IP Forwarding performance (question, and some info) [7-stable, current, em, smp] Message-ID: <20080707224659.B7844@besplex.bde.org> In-Reply-To: <20080707134036.S63144@fledge.watson.org> References: <4867420D.7090406@gtcomm.net> <4869ACFC.5020205@gtcomm.net> <4869B025.9080006@gtcomm.net> <486A7E45.3030902@gtcomm.net> <486A8F24.5010000@gtcomm.net> <486A9A0E.6060308@elischer.org> <486B41D5.3060609@gtcomm.net> <alpine.LFD.1.10.0807021052041.557@filebunker.xip.at> <486B4F11.6040906@gtcomm.net> <alpine.LFD.1.10.0807021155280.557@filebunker.xip.at> <486BC7F5.5070604@gtcomm.net> <20080703160540.W6369@delplex.bde.org> <486C7F93.7010308@gtcomm.net> <20080703195521.O6973@delplex.bde.org> <486D35A0.4000302@gtcomm.net> <alpine.LFD.1.10.0807041106591.19613@filebunker.xip.at> <486DF1A3.9000409@gtcomm.net> <alpine.LFD.1.10.0807041303490.20760@filebunker.xip.at> <486E65E6.3060301@gtcomm.net> <alpine.LFD.1.10.0807052356130.2145@filebunker.xip.at> <4871DB8E.5070903@freebsd.org> <20080707191918.B4703@besplex.bde.org> <4871FB66.1060406@freebsd.org> <20080707213356.G7572@besplex.bde.org> <20080707134036.S63144@fledge.watson.org>
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On Mon, 7 Jul 2008, Robert Watson wrote: > Since you're doing fine-grained performance measurements of a code path that > interests me a lot, could you compare the cost per-send on UDP for the > following four cases: > > (1) sendto() to a specific address and port on a socket that has been bound > to > INADDR_ANY and a specific port. > > (2) sendto() on a specific address and port on a socket that has been bound > to > a specific IP address (not INADDR_ANY) and a specific port. > > (3) send() on a socket that has been connect()'d to a specific IP address and > a specific port, and bound to INADDR_ANY and a specific port. > > (4) send() on a socket that has been connect()'d to a specific IP address > and a specific port, and bound to a specific IP address (not INADDR_ANY) > and a specific port. > > The last of these should really be quite a bit faster than the first of > these, but I'd be interested in seeing specific measurements for each if > that's possible! Not sure if I understand networking well enough to set these up quickly. Does netrate use one of (3) or (4) now? I can tell you vaguely about old results for netrate (send()) vs ttcp (sendto()). send() is lighter weight of course, and this made a difference of 10-20%, but after further tuning the difference became smaller, which suggests that everything ends up waiting for something in common. Now I can measure cache misses better and hope that a simple count of cache misses will be a more reproducible indicator of significant bottlenecks than pps. I got nowhere trying to reduce instruction counts, possibly because it would take avoiding 100's of instructions to get the same benefit as avoiding a single cache miss. Bruce
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