linux-kernel - Re: [patch] fix the softlockup watchdog to actually work

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Date:	Thu, 19 Jul 2007 17:09:55 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...nel.org, Greg KH <greg@...ah.com>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [patch] fix the softlockup watchdog to actually work


* Jeremy Fitzhardinge <jeremy@...p.org> wrote:

> Ingo Molnar wrote:
> > no, the return value after idling can be completely random on some 
> > boxes, on a 64-bit scale - triggering the softlockup watchdog randomly. 
> > (some boxes return random TSC values, etc.) Again, it's fine for the 
> > scheduler's purpose, that's why i named it sched_clock().
> >
> > the proper clocksource use within the kernel is ktime_get() [or 
> > ktime_get_ts()]. Do not abuse sched_clock() for such things.
> 
> Well, my observation is that both softlockup and the scheduler really 
> want to measure unstolen time, so it seemed to me that sched_clock was 
> a nice common place to implement that, rather than implementing a 
> whole new time interface.  At the time that seemed OK, and nobody had 
> any objections.

yeah. But then it should not be using sched_clock() but CFS's new 
rq_clock() method - which does try to construct a globally valid 
timesource out of sched_clock(). [that fix is not backportable though]

	Ingo
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