Date: Thu, 4 Dec 2014 00:49:29 +0100 (CET)
From: Thomas Gleixner <tglx@linutronix.de>
To: Dave Jones <davej@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>, Chris Mason <clm@fb.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>,
        Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        =?ISO-8859-15?Q?D=E2niel_Fraga?= <fragabr@gmail.com>,
        Sasha Levin <sasha.levin@oracle.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        John Stultz <john.stultz@linaro.org>
Subject: Re: frequent lockups in 3.18rc4
In-Reply-To: <20141203232115.GA13266@redhat.com>
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On Wed, 3 Dec 2014, Dave Jones wrote:
> On Wed, Dec 03, 2014 at 11:19:11PM +0100, Thomas Gleixner wrote:
>  > On Wed, 3 Dec 2014, Linus Torvalds wrote:
>  > > On Wed, Dec 3, 2014 at 12:55 PM, Thomas Gleixner <tglx@linutronix.de> wrote:
>  > > >
>  > > > But it's always negative, which means HPET is always ahead of
>  > > > TSC. That excludes pretty much the clocksource watchdog starvation
>  > > > issue which results in TSC being ahead of HPET due to a HPET
>  > > > wraparound (which takes ~300s).
>  > > 
>  > > Still, I'd be more likely to trust the TSC than the HPET on modern
>  > > machines.. And DaveJ's machine isn't some old one.
>  > 
>  > Well, that does not explain the softlock watchdog which is solely
>  > relying on the TSC.
>  > 
>  > > Of course, there's always BIOS games. Can we read the TSC offset
>  > > register and check it being constant (modulo sleep events)?
>  > 
>  > The kernel does not touch it. Here is a untested hack to verify it on
>  > every local apic timer interrupt. Not nice, but simple :)
>  
>  > +			pr_err("TSC adjustment on cpu %d changed %llu -> %llu\n",
>  > +			       cpu,
>  > +			       (unsigned long long) __this_cpu_read(tsc_adjust),
>  > +			       (unsigned long long) adj);
> 
> I just got 
> 
> [ 1472.614433] Clocksource tsc unstable (delta = -26373048906 ns)
> 
> without any sign of the pr_err above.

Bah. Would have been too simple ....

Could you please run Ingos time-warp test on that machine for a while?

   http://people.redhat.com/mingo/time-warp-test/time-warp-test.c

Please change:

- #define TEST_CLOCK 0
+ #define TEST_CLOCK 1

I'll dig further into the time/clocksource whatever related changes
post 3.16

Thanks,

	tglx
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