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 <t...@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.
Dave
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