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Re: [Xen-devel] System time monotonicity

  • To: John Levon <levon@xxxxxxxxxxxxxxxxx>
  • From: Keir Fraser <keir@xxxxxxxxxxxxx>
  • Date: Tue, 27 Mar 2007 11:47:40 +0100
  • Cc: xen-devel@xxxxxxxxxxxxxxxxxxx
  • Delivery-date: Tue, 27 Mar 2007 03:46:51 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AcdwXVcqlZIA8txQEdu1BgAX8io7RQ==
  • Thread-topic: [Xen-devel] System time monotonicity

On 26/3/07 21:04, "John Levon" <levon@xxxxxxxxxxxxxxxxx> wrote:

>> Small backwards time deltas are possible from the current time code. You'll
>> have to filter them out yourself if you can't deal with them. We could add
>> extra code in Xen to stop this happening for any individual VCPU
> Some instrumentation indicated that we had cross-VCPU jitter of
> significant deltas, ~18us at worst. Though the instrumentation wasn't
> completely reliable so that might not be accurate.

I should add that time synchronisation is currently broken in xen-unstable,
and has been for about two weeks. I just checked in a patch (based on one
from Jan Beulich) to fix this (changeset 14573:ba9d3fd4ee4b).

 -- Keir

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