Date: Tue, 09 Nov 2004 10:02:18 -0800 From: Julian Elischer <julian@elischer.org> To: Robert Watson <rwatson@FreeBSD.org> Cc: Stephan Uphoff <ups@tree.com> Subject: Re: cvs commit: src/sys/i386/i386 pmap.c Message-ID: <4191062A.6090009@elischer.org> In-Reply-To: <Pine.NEB.3.96L.1041109103037.73102S-100000@fledge.watson.org> References: <Pine.NEB.3.96L.1041109103037.73102S-100000@fledge.watson.org>
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Robert Watson wrote: >This change made a large difference, and eliminates the unexplained costs. >Here's a revised table as compared to the above: > > sleep mutex crit section spin mutex new spin mutex > UP SMP UP SMP UP SMP UP SMP >PIII 21 81 83 81 112 141 95 141 >P4 39 260 120 119 274 342 132 231 > >So it basically cut 140 cycles off the P4 UP spin lock, 15 off the PIII UP >spin lock, and 110 cycles off the P4 SMP spin lock. The PIII SMP spin >lock looks the same. Keep in mind that all of these measurements have a >standard deviation of between 0 and 3 cycles, most in the 1 range. Also >keep in mind that these are entirely uncontended measurements. > >Assuming that these changes are correct, and pass whatever tests people >have in mind, this would be a very strong merge candidate for performance >reasons. The difference is visible in packet send tests from user space >as a percentage or two improvement on UP on my P4, although it's a litte >hard to tell due to the noise. > > Can you explain why a spin mutex is more expensive than a sleep mutex (I assume this is uncontested)?
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