linux-kernel - Re: frequent lockups in 3.18rc4

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Date:	Wed, 3 Dec 2014 15:09:06 -0500
From:	Dave Jones <davej@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Chris Mason <clm@...com>,
	Mike Galbraith <umgwanakikbuti@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dâniel Fraga <fragabr@...il.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <john.stultz@...aro.org>
Subject: Re: frequent lockups in 3.18rc4

On Wed, Dec 03, 2014 at 11:48:55AM -0800, Linus Torvalds wrote:
 > On Wed, Dec 3, 2014 at 11:25 AM, Linus Torvalds
 > <torvalds@...ux-foundation.org> wrote:
 > >
 > > I don't know. This piece of code:
 > >
 > >         delta = clocksource_delta(wdnow, cs->wd_last, watchdog->mask);
 > >
 > > makes no sense to me.
 > 
 > Yeah, no, I see what's up. I missed that whole wd_last vs cs_last
 > pairing. I guess that part is all good. There are other crazy issues
 > in there, though, like the double test of 'watchdog_reset_pending'. So
 > I still wonder, though, since that odd 96-second delta is just insane
 > and makes no sense from a TSC standpoint (it's closer to a 32-bit
 > overflow of a hpet counter, but that sounds off too).

fwiw, there's quite a bit of variance in the delta that seems to show up.

Clocksource tsc unstable (delta = -1010986453 ns) 
Clocksource tsc unstable (delta = -112130224777 ns) 
Clocksource tsc unstable (delta = -154880389323 ns) 
Clocksource tsc unstable (delta = -165033940543 ns) 
Clocksource tsc unstable (delta = -16610147135 ns) 
Clocksource tsc unstable (delta = -169783264218 ns) 
Clocksource tsc unstable (delta = -183044061613 ns) 
Clocksource tsc unstable (delta = -188697049603 ns) 
Clocksource tsc unstable (delta = -190100649573 ns) 
Clocksource tsc unstable (delta = -192732788150 ns) 
Clocksource tsc unstable (delta = -211622574067 ns) 
Clocksource tsc unstable (delta = -219378634234 ns) 
Clocksource tsc unstable (delta = -226609871873 ns) 
Clocksource tsc unstable (delta = -228355467642 ns) 
Clocksource tsc unstable (delta = -233950238702 ns) 
Clocksource tsc unstable (delta = -243666538341 ns) 
Clocksource tsc unstable (delta = -251535074315 ns) 
Clocksource tsc unstable (delta = -26880030622 ns) 
Clocksource tsc unstable (delta = -37899993747 ns) 
Clocksource tsc unstable (delta = -50471031780 ns) 
Clocksource tsc unstable (delta = -6821168015 ns) 
Clocksource tsc unstable (delta = -7067883139 ns)
Clocksource tsc unstable (delta = -76682050692 ns) 
Clocksource tsc unstable (delta = -8296489689 ns) 
Clocksource tsc unstable (delta = -88373866635 ns) 
Clocksource tsc unstable (delta = -89099193219 ns) 
Clocksource tsc unstable (delta = -95946009388 ns) 


(sort -u'ed post grep, the ordering here doesn't mean anything)

	Dave
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