Date: Tue, 4 Jan 2011 11:40:12 GMT From: Colin Percival <cperciva@freebsd.org> To: freebsd-xen@FreeBSD.org Subject: Re: kern/153620: [xen] Xen guest system clock drifts in AWS EC2 (FreeBSD 9.0-CURRENT i386 T1-micro) Message-ID: <201101041140.p04BeCXx074589@freefall.freebsd.org>
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The following reply was made to PR kern/153620; it has been noted by GNATS. From: Colin Percival <cperciva@freebsd.org> To: bug-followup@FreeBSD.org, fbsd-9.0-aws-ec2-1293964000@holmberg.to Cc: Subject: Re: kern/153620: [xen] Xen guest system clock drifts in AWS EC2 (FreeBSD 9.0-CURRENT i386 T1-micro) Date: Tue, 04 Jan 2011 03:32:21 -0800 Ok, I think I see what's happening here: Under some conditions it seems that the clock stops running. If there are no interrupts from any source, the FreeBSD instance never gets scheduled; and the clock loses time in multiples of the timecounter period (2^41 ns) if it doesn't tick for that long. The reason this doesn't show up with an interactive login session open is that ssh generates enough network traffic to wake the kernel periodically; this is also provides a workaround for this bug: Send a ping to the instance once every 30 minutes. -- Colin Percival Security Officer, FreeBSD | freebsd.org | The power to serve Founder / author, Tarsnap | tarsnap.com | Online backups for the truly paranoid
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