Re: [patch 1/4] Ignore stolen time in the softlockup watchdog

From: Jeremy Fitzhardinge
Date: Tue Apr 24 2007 - 02:58:16 EST

Andrew Morton wrote:
> On Tue, 27 Mar 2007 14:49:20 -0700 Jeremy Fitzhardinge <jeremy@xxxxxxxx> wrote:
>> The softlockup watchdog is currently a nuisance in a virtual machine,
>> since the whole system could have the CPU stolen from it for a long
>> period of time. While it would be unlikely for a guest domain to be
>> denied timer interrupts for over 10s, it could happen and any softlockup
>> message would be completely spurious.
>> Earlier I proposed that sched_clock() return time in unstolen
>> nanoseconds, which is how Xen and VMI currently implement it. If the
>> softlockup watchdog uses sched_clock() to measure time, it would
>> automatically ignore stolen time, and therefore only report when the
>> guest itself locked up. When running native, sched_clock() returns
>> real-time nanoseconds, so the behaviour would be unchanged.
>> Note that sched_clock() used this way is inherently per-cpu, so this
>> patch makes sure that the per-processor watchdog thread initialized
>> its own timestamp.
> This patch
> (
> causes six failures in the locking self-tests, which I must say is rather
> clever of it.

Interesting. Which variation of sched_clock do you have in your tree at
the moment?

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