Date: Sat, 24 Nov 2007 20:19:34 +0100 From: Kris Kennaway <kris@FreeBSD.org> To: Max Laier <max@love2party.net> Cc: freebsd-net@freebsd.org, freebsd-current@freebsd.org, Robert Watson <rwatson@freebsd.org> Subject: Re: Switch pfil(9) to rmlocks Message-ID: <47487946.2010202@FreeBSD.org> In-Reply-To: <200711242006.04753.max@love2party.net> References: <200711231232.04447.max@love2party.net> <20071123132453.W98338@fledge.watson.org> <200711242006.04753.max@love2party.net>
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Max Laier wrote: > On Friday 23 November 2007, Robert Watson wrote: >> On Fri, 23 Nov 2007, Max Laier wrote: >>> attached is a diff to switch the pfil(9) subsystem to rmlocks, which >>> are more suited for the task. I'd like some exposure before doing >>> the switch, but I don't expect any fallout. This email is going >>> through the patched pfil already - twice. >> Max, >> >> Have you done performance measurements that show rmlocks to be a win in >> this scenario? I did some patchs for UNIX domain sockets to replace >> the rwlock there but it appeared not to have a measurable impact on SQL >> benchmarks, presumbaly because the read/write blend wasn't right and/or >> that wasnt a significant source of overhead in the benchmark. I'd >> anticipate a much more measurable improvement for pfil, but would be >> interested in learning how much is seen? > > I had to roll an artificial benchmark in order to see a significant change > (attached - it's a hack!). > > Using 3 threads on a 4 CPU machine I get the following results: > null hook: ~13% +/- 2 > mtx hook: up to 40% [*] > rw hook: ~5% +/- 1 > rm hook: ~35% +/- 5 > > [*] The mtx hook is inconclusive as my measurements vary a lot. If one > thread gets lucky and keeps running the overall time obviously goes down > by a magnitude. It seems however, that rmlocks greatly increase the > chance of that happening - not sure if that's a good thing, though. If > all threads receive approximately equal runtime (which is almost always > the case for rwlocks) the difference is somewhere around 10%. Is that something we can try to arrange to happen for improved performance in more general situations? Kris
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