Date: Thu, 19 Jan 2012 20:04:34 +0000 From: Joe Holden <lists@rewt.org.uk> To: Ian Lepore <freebsd@damnhippie.dyndns.org> Cc: FreeBSD Stable Mailing List <freebsd-stable@freebsd.org> Subject: Re: Timekeeping in stable/9 Message-ID: <4F187752.80409@rewt.org.uk> In-Reply-To: <1326913229.1669.281.camel@revolution.hippie.lan> References: <4F15D643.8000907@rewt.org.uk> <1326913229.1669.281.camel@revolution.hippie.lan>
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Looks like this is down to the dynamic/tickless changes in 9 (that aren't even noted in the release notes), the machines have now been switched to linux as the lack of responses/care given to my recent postings has been noted and it was deemed that using linux would be less hassle in the long run. Unfortunate decision but I am inclined to agree. Thanks, J Ian Lepore wrote: > On Tue, 2012-01-17 at 20:12 +0000, Joe Holden wrote: >> Hi guys, >> >> Has anyone else noticed the tendency for 9.0-R to be unable to >> accurately keep time? I've got a couple of machines that have been >> upgraded from 8.2 that are struggling, in particular a Virtual box guest >> that was fine on 8.2, but now that's its been upgraded to 9.0 counts at >> anything from 2 to 20 seconds per 5 second sample, the result is similar >> with HPET, ACPI-fast and TSC. >> >> I also have physical boxes which new seem to drift quite substantially, >> ntpd cannot keep up and as these boxes need to be able to report the >> time relatively accurately, it is causing problems with log times and >> such... >> >> Any suggestions most welcome! >> >> Thanks, >> J > > I finally got a 9.0 generic build done today and I've been watching the > timekeeping on 3 systems and they're all doing just fine. Two of the > systems are performing pretty much identically to how they did on 8.2; > the clock frequency correction calculated by ntpd differs by less than > 1ppm. On the other system the kernel timekeeping routines are now > choosing to use a different clock so I don't get a direct comparison of > the old vs new drift rate, but the drift is still reasonable (100ppm > now, used to be around 88, on an old 300mhz MediaGx-based system). > > I haven't had time yet to learn about the new eventtimer stuff in 9.0, > but I know you can get some info on the choices it made via sysctl > kern.eventtimer. Before 9.0 I'd check sysctl kern.clockrate and vmstat > -i and make sure the chosen clock is interrupting at the right rate, but > now with the eventtimer stuff there's not an obvious correlation between > hz and profhz and stathz and any particular device's interrupt rate, at > least for some clock choices (on the old MediaGx system without ACPI or > HPET it seems to work more like it used to). > > -- Ian > >
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