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RE: Xen system skew MUCH worse than tsc skew (was RE: [Xen-devel]RE: [PATCH] record max stime skew (was RE: [PATCH] strictly increasinghvm guest time))


  • To: <dan.magenheimer@xxxxxxxxxx>, "Keir Fraser" <keir.fraser@xxxxxxxxxxxxx>, "Xen-Devel (E-mail)" <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
  • Date: Wed, 23 Jul 2008 14:11:51 +0800
  • Cc: Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>
  • Delivery-date: Tue, 22 Jul 2008 23:14:07 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcjcXTkqnSPaEESHRsmD1HhwJkyawAAAIPEpAAuAJ0AAAgl0IAAT2dqMABFKNxAAAHEqUAAGNaGwAAdfXjQAIb9HAAAAjWJ4AAico9AAAPZ0lAECdtJAABGXRyYAHMJkcAAXKn0wAaR9gGAAUpgMiQBOeNLwABESLpA=
  • Thread-topic: Xen system skew MUCH worse than tsc skew (was RE: [Xen-devel]RE: [PATCH] record max stime skew (was RE: [PATCH] strictly increasinghvm guest time))

>From: Dan Magenheimer
>Sent: 2008年7月23日 6:27
>
>Perhaps some form of the proposed "deferrable timers" can
>be used to ensure per-cpu calibration happens on different
>processors at roughly the same moment?
>

It can't. Deferrable timer is a per-cpu concept, to rendezvous
what can be deferred on local cpu. There's nothing to 
coordinate across-cpu activities, for which Instead you have to 
use some form of IPIs and self-defined sync process as what
Ian suggested.

Thanks,
Kevin

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