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xen-devel
Re: [Xen-devel] [patch 14/33] xen: xen time implementation
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To: |
Jan Beulich <jbeulich@xxxxxxxxxx> |
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Subject: |
Re: [Xen-devel] [patch 14/33] xen: xen time implementation |
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From: |
Keir Fraser <keir@xxxxxxxxxxxxx> |
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Date: |
Wed, 06 Jun 2007 12:52:59 +0100 |
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Cc: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, lkml <linux-kernel@xxxxxxxxxxxxxxx>, Andi Kleen <ak@xxxxxxx>, Chris Wright <chrisw@xxxxxxxxxxxx>, virtualization@xxxxxxxxxxxxxx, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxx> |
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Wed, 06 Jun 2007 04:51:11 -0700 |
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[Xen-devel] [patch 14/33] xen: xen time implementation |
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On 6/6/07 12:00, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
>> If the error across CPUS is +/- just a few microseconds at worst then having
>> the clocksource clamp to no less than the last timestamp returned seems a
>> reasonable fix. Time won't 'stop' for longer than the cross-CPU error, and
>> that should always be a tiny value.
>
> Are you sure this is also true when e.g. a CPU gets throttled due to thermal
> conditions? It is my understanding that both the duty cycle adjustment and
> the frequency reduction would yield a reduced rate TSC, which would be
> accounted for only the next time the local clock gets calibrated. Otherwise,
> immediate calibration (and vcpu update) would need to be forced out of the
> thermal interrupt.
Yes, this could be an issue. Is there any way to get an interrupt or MCE
when thermal throttling occurs?
-- Keir
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