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

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Message-ID: <20100326180025.052d930f@penta.localdomain>
Date:	Fri, 26 Mar 2010 18:00:25 -0400
From:	Yury Polyanskiy <ypolyans@...nceton.edu>
To:	Joel Becker <Joel.Becker@...cle.com>
Cc:	linux-kernel@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	john stultz <johnstul@...ibm.com>,
	Jan Glauber <jan.glauber@...ibm.com>
Subject: Re: [PATCH] hangcheck-timer is broken on x86

On Fri, 26 Mar 2010 14:46:49 -0700
Joel Becker <Joel.Becker@...cle.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.

> 
> 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.

Yury

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