Date: Wed, 01 Jun 2011 08:40:33 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Jung-uk Kim <jkim@FreeBSD.org> Cc: freebsd-hackers@FreeBSD.org Subject: Re: [RFC] Enabling invariant TSC timecounter on SMP Message-ID: <4DE5D0D1.1030903@FreeBSD.org> In-Reply-To: <201105311616.31256.jkim@FreeBSD.org> References: <201105241356.45543.jkim@FreeBSD.org> <4DE4CE82.4030301@FreeBSD.org> <201105311616.31256.jkim@FreeBSD.org>
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on 31/05/2011 23:16 Jung-uk Kim said the following: > On Tuesday 31 May 2011 07:18 am, Andriy Gapon wrote: >> on 24/05/2011 20:56 Jung-uk Kim said the following: >>> I think it's about time to enable invariant TSC timecounter on >>> SMP by default. Please see the attached patch. It is also >>> available from here: >>> >>> http://people.freebsd.org/~jkim/tsc_smp_test4.diff >>> >>> avg convinced me enough that it should be an opt-out feature >>> going forward. :-) >> >> Not sure if I really did that. >> My position is this: >> - if we think that TSC is SMP-safe then it should have the best >> priority >> - we should do our best to auto-guess if TSC is SMP-safe >> unless a user explicitly overrides that property (either via >> explicit testing or by making guesses based on CPU model or etc) > > I am sorry if I misunderstood your intention. However, I added > explicit boot-time TSC sanity check (to do our best to auto-guess) > and I think TSC is fairly SMP-safe. Hence, I thought that it is > about time for the change. In this case - yes. But I remember that you were thinking about either improving or simplifying that check or both. >>> Comments? >> >> Perhaps I missed it, but I don't remember the "lowres" part of the >> patch being discussed. > > No, it wasn't discussed with you. Do you see any problem with that > code? I don't see any obvious problem, but I also don't understand rationale of using smaller max_freq for the ncpus > 1 case. Maybe these two logical changes should be done as two separate commits. -- Andriy Gapon
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