Date: Wed, 15 Feb 2006 12:30:43 -0800 From: Luigi Rizzo <rizzo@icir.org> To: Andre Oppermann <andre@freebsd.org> Cc: Marcos Bedinelli <bedinelli@madhaus.cns.utoronto.ca>, Max Laier <max@love2party.net>, Julian Elischer <julian@elischer.org>, freebsd-net@freebsd.org Subject: Re: Network performance in a dual CPU system Message-ID: <20060215123043.A29559@xorpc.icir.org> In-Reply-To: <43F38CF5.71C326C1@freebsd.org>; from andre@freebsd.org on Wed, Feb 15, 2006 at 09:20:05PM %2B0100 References: <7bb8f24157080b6aaacb897a99259df9@madhaus.cns.utoronto.ca> <711b7ec873f31bc5be50ce477313fac3@madhaus.cns.utoronto.ca> <200602110002.21275.max@love2party.net> <43F38CF5.71C326C1@freebsd.org>
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On Wed, Feb 15, 2006 at 09:20:05PM +0100, Andre Oppermann wrote: ... > >From my profiling with the Agilent tester there seem to be two areas where > the packet filters (ipfw in my test case) burn a lot of CPU per packet. > That is a) setup of lots of packet variables unconditionally at the entry > of ip_fw_chk() no matter whether they get looked at later or not, and b) > the switch() going through all the packet inspection options is for some > reason not optimized by the compiler and burns even more CPU. Some sort > of JIT (as in the new bpf code) which replaces the case testing and jumps > directly to the proper place in the switch statement would go a long way > of making it way more performant. i was expecting some overhead in the initial setting of variables but the cost of the switch() surprises me a bit. did you look at the assembly code produced, or otherwise could you explain a bit more how you think the switch affects performance ? Maybe one could make it cheaper through an indirect function call ? (in the end, instructions are already indexes for a jump table). cheers luigi
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