linux-kernel - Re: [GIT PULL] TSC sched

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Date:	Fri, 11 Nov 2011 08:06:15 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	John Stultz <johnstul@...ibm.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	lkml <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [GIT PULL] TSC sched_clock overflow workaround


* John Stultz <johnstul@...ibm.com> wrote:

> Hey Thomas, Ingo,
> 	I thought Peter had sent this on, but apparently its not landed yet, so
> I wanted to make sure you got it.
> 
> After ~208 days, the sched_clock multiplication overflows and 
> causes some false positives in the softlockup watchdog. I don't 
> think there are any actual panics going on, as an earlier related 
> div by zero issue was already fixed. However, the false positives 
> do continue to worry folks.
> 
> We still need a proper fix, which will probably be in part making 
> sched_clock do periodic accumulation, as well as possibly changing 
> users of sched_clock (like the softlockup watchdog) use timekeeping 
> timestamps rather then sched_clock.

I'd *much* rather see a real fix for this than an ugly workaround 
that disables a very real speedup.

Thanks,

	Ingo
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