Date: Mon, 24 May 2004 08:31:30 +0200 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Bruce Evans <bde@zeta.org.au> Cc: Nate Lawson <nate@root.org> Subject: Re: cvs commit: src/sys/conf files.amd64 Message-ID: <9717.1085380290@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 24 May 2004 16:26:28 %2B1000." <20040524155045.V23809@gamplex.bde.org>
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In message <20040524155045.V23809@gamplex.bde.org>, Bruce Evans writes: >> I agree and think it may be good to do something about this. Care to >> suggest a way to adjust or at least detect TSC rate changes? On my >> laptop, the switch from 1 Ghz to 733 Mhz is done via SMM and thus is not >> user-detectable except through profiling. However, on desktop systems, >> the switch is almost certainly never automatic. We can have the control >> system notify the timecounters when the rate changes. > >The TSC could be sample on every clock interrupt or on every timecounter >call. This should at least tell you if the average TSC rate for the >samping period was significantly different, and if there is any long-term >drift. If the TSC varies in frequency we should not use it for timecounting, trying to compensate for the changes will never be precise enough to avoid significant short term jitter. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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