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

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Message-ID: <20070725090439.GA26286@elte.hu>
Date:	Wed, 25 Jul 2007 11:04:39 +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:

> >  softlockup-add-irq-regs-h.patch
> >  softlockup-better-printout.patch
> >  softlockup-cleanups.patch
> >  softlockup-use-cpu-clock.patch
> > 
> > they are all necessary.
> 
> I think I have.  Seems that someone hasn't been naming their patches
> consistently (which is quite irksome).  I have:
> 
> fix-the-softlockup-watchdog-to-actually-work.patch
> softlockup-make-asm-irq_regsh-available-on-every-platform.patch
> softlockup-improve-debug-output.patch
> softlockup-watchdog-style-cleanups.patch
> softlockup-add-a-proc-tuning-parameter.patch
> softlockup-add-a-proc-tuning-parameter-fix.patch

you have the key one missing i think - attached below.

	Ingo

------------------------------------>
Subject: softlockup: use cpu_clock() instead of sched_clock()
From: Ingo Molnar <mingo@...e.hu>

sched_clock() is not a reliable time-source, use cpu_clock() instead.

Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/softlockup.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Index: linux/kernel/softlockup.c
===================================================================
--- linux.orig/kernel/softlockup.c
+++ linux/kernel/softlockup.c
@@ -42,14 +42,16 @@ static struct notifier_block panic_block
  * resolution, and we don't need to waste time with a big divide when
  * 2^30ns == 1.074s.
  */
-static unsigned long get_timestamp(void)
+static unsigned long get_timestamp(int this_cpu)
 {
-	return sched_clock() >> 30;  /* 2^30 ~= 10^9 */
+	return cpu_clock(this_cpu) >> 30;  /* 2^30 ~= 10^9 */
 }
 
 void touch_softlockup_watchdog(void)
 {
-	__raw_get_cpu_var(touch_timestamp) = get_timestamp();
+	int this_cpu = raw_smp_processor_id();
+
+	per_cpu(touch_timestamp, this_cpu) = get_timestamp(this_cpu);
 }
 EXPORT_SYMBOL(touch_softlockup_watchdog);
 
@@ -95,7 +97,7 @@ void softlockup_tick(void)
 		return;
 	}
 
-	now = get_timestamp();
+	now = get_timestamp(this_cpu);
 
 	/* Wake up the high-prio watchdog task every second: */
 	if (now > (touch_timestamp + 1))
-
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