Date: Sat, 29 Oct 2005 11:09:51 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: "M. Warner Losh" <imp@bsdimp.com> Cc: pertti.kosunen@pp.nic.fi, phk@phk.freebsd.dk, davidxu@FreeBSD.org, jura@networks.ru, current@FreeBSD.org Subject: Re: Timers and timing, was: MySQL Performance 6.0rc1 Message-ID: <20051029110825.B20147@fledge.watson.org> In-Reply-To: <20051028.221825.90826015.imp@bsdimp.com> References: <35696.1130538037@critter.freebsd.dk> <20051029005719.I20147@fledge.watson.org> <4362CBC2.8050602@freebsd.org> <20051028.221825.90826015.imp@bsdimp.com>
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On Fri, 28 Oct 2005, M. Warner Losh wrote: > : 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. > > And unfortuantely, the argument that needs to be passed to abstime is > unspecified, at leas tin our man page. Also unfortuantely, > CLOCK_REALTIME seems to be what's required here (our man page just says > 'if the system time reaches the time specified in abstime'), rather than > CLOCK_MONOTONIC so jumps in system time can cause previously short > timeouts to become rather large timeouts... This is a flaw in the API. > :-( If the assumption is that these calls will behave like select() and poll(), then I would guess lowering the accuracy here would not be a problem, since it is widely understand that select() waits at timer tick granularity. Robert N M Watson
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