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

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Message-ID: <20100327005710.GA31009@mail.oracle.com>
Date:	Fri, 26 Mar 2010 17:57:11 -0700
From:	Joel Becker <Joel.Becker@...cle.com>
To:	Yury Polyanskiy <ypolyans@...nceton.edu>
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, Mar 26, 2010 at 06:00:25PM -0400, Yury Polyanskiy wrote:
> 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.

	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@...cle.com>

Joel

-- 

Dort wo man Bücher verbrennt, verbrennt man am Ende auch Mensch.
(Wherever they burn books, they will also end up burning people.)
	- Heinrich Heine

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