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Re: [Xen-devel] [timer/ticks related] dom0 hang during boot on large 1TB

To: Jan Beulich <JBeulich@xxxxxxxxxx>, Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>, "mukesh.rathor@xxxxxxxxxx" <mukesh.rathor@xxxxxxxxxx>
Subject: Re: [Xen-devel] [timer/ticks related] dom0 hang during boot on large 1TB system
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 22 Dec 2009 17:48:36 +0000
Cc: "kurt.hackel@xxxxxxxxxx" <kurt.hackel@xxxxxxxxxx>, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, "Xen-devel@xxxxxxxxxxxxxxxxxxx" <Xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 22/12/2009 16:42, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>>>> "Jan Beulich" <JBeulich@xxxxxxxxxx> 22.12.09 17:33 >>>
>> One other irregular at the first glance thing is that the mentioned
>> very first run through time_calibration() does not seem to result in
>> running local_time_calibration() on CPU0. One invocation (apparently
>> independent of time_calibration()) happens right before Dom0 starts
>> executing.
> And that's of course the problem: CPU0's TIME_CALIBRATE_SOFTIRQ can't
> get serviced until entry to Dom0, but CPU0 is responsible for re-arming
> calibration_timer. Hence there's a gap of calibrations, resulting in an
> excessive delta observed during the first timer interrupt in Dom0.

Arbitrarily delaying softirq work is probably inherently fragile. All we
have to defer is SCHEDULE_SOFTIRQ as that can preempt the current context.
So I will look into making a patch that changes process_pending_timers() to


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