Date: Mon, 06 Dec 2010 19:58:25 +0200 From: Andriy Gapon <avg@freebsd.org> To: Jung-uk Kim <jkim@freebsd.org> Cc: freebsd-current@freebsd.org Subject: Re: non-invariant tsc and cputicker Message-ID: <4CFD2441.5090408@freebsd.org> In-Reply-To: <201012061243.08577.jkim@FreeBSD.org> References: <4CF92852.20705@freebsd.org> <201012031938.12684.jkim@FreeBSD.org> <4CFA220A.30405@freebsd.org> <201012061243.08577.jkim@FreeBSD.org>
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on 06/12/2010 19:42 Jung-uk Kim said the following: > Sigh... Please see the history of calcru() in > sys/kern/kern_resource.c. Most important ones are: > > http://svn.freebsd.org/viewvc/base?view=revision&revision=155444 > http://svn.freebsd.org/viewvc/base?view=revision&revision=155534 > > Basically, we chose efficiency over accuracy and you are suggesting > going backwards. Well, I guess that it depends. Looking at r155444 - the time is still going to be accounted in ticks (but timecounter ticks). BTW, I think that this quote says something: "On more modern hardware no change in performance is seen." and that was ~5 years ago. Looking at r155534 - the only change that is going to get undone is using TSC for the accounting ticks, and that is only for machines with non-invariant TSC. And I think that all sufficiently modern machines have invariant TSC and, in Intel's words, that's an architectural path going forward. So, I don't think that I propose a dramatic change. -- Andriy Gapon
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