On Fri, 5 Jul 2013, Peter Zijlstra wrote:
> On Fri, Jul 05, 2013 at 04:23:33PM +0200, Frederic Weisbecker wrote:
> > Nope, I haven't touched that. I prefer not to fiddle with unstable
> > clocksource for now :)
> >
> > As for unstable TSCs, if sched_clock_tick() needs to be fed, we simply
> > don't stop the tick.
>
> Not entirely the same thing; I thought the clocksource watchdog was ran
> even when we have a 'stable' TSC, just to make sure it stays stable.
> There's known cases where the BIOS f*cks us over and wrecks TSC sync.
See arch/x86/kernel/tsc.c
We disable the watchdog for the TSC when tsc_clocksource_reliable is
set.
tsc_clocksource_reliable is set when:
- you add tsc=reliable to the kernel command line
- boot_cpu_has(X86_FEATURE_TSC_RELIABLE)
X86_FEATURE_TSC_RELIABLE is a software flag, set by vmware and
moorsetown. So all other machines keep the watchdog enabled.
- On Geode LX (OLPC)
Thanks,
tglx
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