Date: Fri, 16 Jul 2010 14:27:44 -0700 From: Rob Farmer <rfarmer@predatorlabs.net> To: Bruce Cran <brucec@muon.cran.org.uk> Cc: Alexander Motin <mav@freebsd.org>, current <current@freebsd.org> Subject: Re: Clock not moving in virtual machine Message-ID: <AANLkTikh7K-yDyHubMLXGDGBZvEmzE0PUubba5fAOJMr@mail.gmail.com> In-Reply-To: <20100716210500.GA13257@muon.cran.org.uk> References: <mailpost.1279239004.5520450.26216.mailing.freebsd.current@FreeBSD.cs.nctu.edu.tw> <4C3FFD3F.7060909@FreeBSD.org> <AANLkTilCKUtVEiViEN_EoCMGl7KvryVXEd-sWuxFjzsS@mail.gmail.com> <4C40C55B.8040508@FreeBSD.org> <20100716210500.GA13257@muon.cran.org.uk>
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On Fri, Jul 16, 2010 at 2:05 PM, Bruce Cran <brucec@muon.cran.org.uk> wrote: > On Fri, Jul 16, 2010 at 11:47:23PM +0300, Alexander Motin wrote: >> >> It is probably hard to see pattern due to to very high clock frequency. >> But TSC timecounter is unreliable even on real SMP systems. What it >> counts on virtual SMP - even bigger question. As system seems never uses >> timecounters with negative quality - you've left with >> kern.timecounter.hardware=dummy - that's why time is not going. As last >> resort you may try to set sysctl kern.timecounter.hardware=TSC in run time. > > I came across the same problem on rootbsd a few days ago, and set the TSC > as the timecounter in /etc/sysctl.conf - I've since found it should be > possible to also set kern.timecounter.smp_tsc=1 in /boot/loader.conf to let > the TSC be chosen. The system's now been running for a day and I've not had > any warnings about the clock going backward, and since the time has > remained correct I guess Xen synchronises with the host? Should I still > switch back to using the i8254? > > -- > Bruce Cran > Setting kern.timecounter.smp_tsc=1 works for me. I put it in /boot/loader.conf so it would automatically work for single user mode too. I don't think the host automatically synchronizes the clock - their website recommends running ntp and I saw the clock drift a fair amount before I started doing that. Thanks for the tip. -- Rob Farmer
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