Date: Mon, 06 Dec 2010 21:38:09 +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: <4CFD3BA1.8080901@freebsd.org> In-Reply-To: <201012061429.08085.jkim@FreeBSD.org> References: <4CF92852.20705@freebsd.org> <201012061401.17904.jkim@FreeBSD.org> <4CFD34E1.40008@freebsd.org> <201012061429.08085.jkim@FreeBSD.org>
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on 06/12/2010 21:27 Jung-uk Kim said the following: > On Monday 06 December 2010 02:09 pm, Andriy Gapon wrote: >> on 06/12/2010 21:01 Jung-uk Kim said the following: >>> :-) Don't get me wrong, I generally agree with you *iff* it does >>> : not >>> >>> hurt too much. Anyway, this issue should be resolved from the >>> root, i.e., kern_resouce.c, if possible. >> >> But what to resolve there? > > Better algorithm for stat. > >> I just want to always have a stable source "cpu ticks", and then >> everything else should just work? > > If we had one, yes. But we don't, at least for old x86 hardware. :-( This sounds contradictory... I don't follow. So, TSC as a direct source of cpu ticks is good enough, but TSC as a source for timecounter acting as a source for cpu ticks is not stable? >> BTW, if someone comes up with a patch for more or less correct >> accounting when "cpu ticks" frequency is allowed to change, then I >> am all for it. But, IMO, it's just easier to use stable "cpu >> ticks". > > If it doesn't hurt too much, yes. Remember the P-state invariant CPUs > are pretty new. Well, not that new in this fast changing world. > SMP-correct TSC is quite rare if there is any. This contradicts my experience. All systems that I could test have "SMP-correct TSC". Yes, they all are 1-2 years old and they all are single-package multi-core systems. I tested only one two-socket machine from perf-cluster and it had more or less "SMP-correct TSC" too. BTW: http://people.freebsd.org/~avg/tsc/ But, this SMP-correctness is not a requirement for the cpu ticks accounting that we are discussing, right? -- Andriy Gapon
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