[GIT PULL] TSC sched_clock overflow workaround

[GIT PULL] TSC sched_clock overflow workaround

[John Stultz]

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.

thanks
-john


Peter's workaround is available in the git repository at:
  git://git.linaro.org/people/jstultz/linux.git fortglx/3.2/tip/sched/clock

Peter Zijlstra (1):
      x86, intel: Don't mark sched_clock() as stable

 arch/x86/kernel/cpu/intel.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

Re: [GIT PULL] TSC sched_clock overflow workaround

[Ingo Molnar]

* John Stultz <johnstul@us.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