Date: Thu, 23 Nov 2006 16:56:55 +0100 From: Ivan Voras <ivoras@fer.hr> To: freebsd-arch@freebsd.org Subject: Re: What is the PREEMPTION option good for? Message-ID: <ek4gc8$492$1@sea.gmane.org> In-Reply-To: <ejnvfo$tv2$1@sea.gmane.org> References: <20061119041421.I16763@delplex.bde.org> <ejnvfo$tv2$1@sea.gmane.org>
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Ivan Voras wrote: > Bruce Evans wrote: > >> Most of the difference is caused by pgzero becoming too active with >> PREEMPTION. > > Don't know about the other things but I've noticed pagezero is > suspiciously active on heavy loaded SMP web servers (even complained on > @stable a long time ago). I'll try disabling PREEMPTION and see how it goes. Ok, I couldn't run extensive tests because people were waiting to use the machine, so this should be considered anecdotal evidence. On a simple benchmark that repeatedly (for 1 minute) and concurrently (target=50 concurrent requests) hits a dynamic web page on a development machine (2 proc true SMP), the performance goes up from ~85 requests/sec. to ~105 requests/s by disabling PREEMPTION. This improvement looks suspiciously high to me, but I don't think I'll be going back :) pagezero is now not noticable in 'top' output.
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