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

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Message-ID: <20100327220355.GA1810@mail.oracle.com>
Date:	Sat, 27 Mar 2010 15:03:55 -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 10:02:59PM -0400, Yury Polyanskiy wrote:
> Joel, just realized there is a slight mistake in what I said before.
> getrawmonotonic() is a refined jiffies (and actually resolves to
> get_cycles() on my system in the end). Thus it doesn't count while in
> suspend. However, jiffies-based timers (aka timer-wheel) are also
> stopped while in suspend. So getrawmonotonic() is the right call to
> check the precision of the jiffies-based timer (i.e. you dont need to
> make a correction by calling monotonic_to_bootbased()). 

	It's OK to tell hangcheck-timer users that suspend is not
allowed.  After all, you're running something that you don't want to see
hang.
	Is there a clock in the system that is a true wallclock?  I'm
guessing, since getrawmonotonic() is get_cycles() based, that it doesn't
provide accurate time in the face of cpufreq changes.  Is that true?

Joel



-- 

Life's Little Instruction Book #497

	"Go down swinging."

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