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

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Message-ID: <20070719075152.GB12760@elte.hu>
Date:	Thu, 19 Jul 2007 09:51:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jeremy Fitzhardinge <jeremy@...p.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


* Andrew Morton <akpm@...ux-foundation.org> wrote:

> But I'll sit on this patch for a while until this gets sorted out. 
> Meanwhile, please double-check the elapsed-time arithmetic in there, 
> maybe do a bit of runtime testing?

btw., could you apply the patch below as well? Maybe sched_clock() is 
misbehaving on your box? (with this i have 5 softlockup patches in my 
tree - and they are working fine so far.)

	Ingo

---------------->
Subject: [patch] softlockup: use a reliable global time source
From: Ingo Molnar <mingo@...e.hu>

using sched_clock() for the soft-lockups was a bad idea, sched_clock()
is not a reliable global time-source.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/softlockup.c |    6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

Index: linux/kernel/softlockup.c
===================================================================
--- linux.orig/kernel/softlockup.c
+++ linux/kernel/softlockup.c
@@ -37,13 +37,11 @@ static struct notifier_block panic_block
 };
 
 /*
- * Returns seconds, approximately.  We don't need nanosecond
- * resolution, and we don't need to waste time with a big divide when
- * 2^30ns == 1.074s.
+ * Returns seconds.
  */
 static unsigned long get_timestamp(void)
 {
-	return sched_clock() >> 30;  /* 2^30 ~= 10^9 */
+	return jiffies / HZ;
 }
 
 void touch_softlockup_watchdog(void)
-
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