Date: Sat, 29 Oct 2005 09:09:22 +0800 From: David Xu <davidxu@freebsd.org> To: Robert Watson <rwatson@FreeBSD.org> Cc: Pertti Kosunen <pertti.kosunen@pp.nic.fi>, Poul-Henning Kamp <phk@phk.freebsd.dk>, current@freebsd.org, "Yuriy N. Shkandybin" <jura@networks.ru> Subject: Re: Timers and timing, was: MySQL Performance 6.0rc1 Message-ID: <4362CBC2.8050602@freebsd.org> In-Reply-To: <20051029005719.I20147@fledge.watson.org> References: <35696.1130538037@critter.freebsd.dk> <20051029005719.I20147@fledge.watson.org>
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Robert Watson wrote: > Another important question is whether using these alternative time > access methods in user space improves the performance of any of the > applications we care about. Hence providing a patch that someone can > try -- while the microbenchmarks seem to show improved performance, > will the applications? I suspect it will in some important cases, but > there's only one way to find out. > > It strikes me that replacing time(3) with something that retrieves > CLOCK_SECOND shouldn't harm time(3) semantics. Likewise, keeping > CLOCK_REALTIME as is is likely OK -- if an application requests it > using clock_gettime(), then it is presumably looking for high > accuracy. It's gettimeofday() that's the troubling one -- it's widely > used to query the time in applications, and its API suggests > microsecond resolution. > > Robert N M Watson > > thread libraries use clock_gettime, this becauses there is pthread_cond_timedwait and other synchronization objects like rwlock, and mutex all have a timeout version, I think pthread_cond_timedwait is mostly used in some applications, though normally, application is not looking for high accuracy. they will get benefit from the clock_gettime speed improvement.
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