Re: [PATCH] hangcheck-timer is broken on x86

Joel Becker
2010-03-27T00:58:28Z

On Fri, Mar 26, 2010 at 06:00:25PM -0400, Yury Polyanskiy wrote:
> On Fri, 26 Mar 2010 14:46:49 -0700
> Joel Becker <Joel.Becker@oracle.com> wrote:
>
> > On Tue, Mar 23, 2010 at 11:36:11PM -0400, Yury Polyanskiy wrote:
>
> > 1) Does getrawmonotonic() satisfy hangcheck-timer? What I mean is, will
> > it always return the wallclock nanoseconds even in the face of CPU speed
> > changes, suspend, udelay, or any other suspension of kernel operation?
> > Yes, I know this is a tougher standard than rdtsc(), but this is what
> > hangcheck-timer wants. rdtsc() at least satisfied udelay and PCI hangs.
>
> Yes, as far as I can tell. Note that rdtsc is hosed on suspend-resume.

Yeah, I know. rdtsc hangcheck-timer really required no suspend
or cpufreq. Since it is only really used by servers, this wasn't a
terrible restriction. Then virtualization came along...

> > 2) If it does satisfy, why not use it for all hangcheck usage instead of
> > any ifdefs?
>
> On my part, I didn't want to touch the S390 code since I can't test it.

Makes sense. Andrew, would you mind pushing this through your
tree?

Acked-by: Joel Becker <joel.becker@oracle.com>

Joel

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Joel Becker
Principal Software Developer
Oracle
E-mail: joel.becker@oracle.com
Phone: (650) 506-8127