RE: [PATCH] configure HAVE_UNSTABLE_SCHED_CLOCK for SGI_SN systems

Peter Zijlstra
2009-01-06T20:57:20Z

On Tue, 2009-01-06 at 12:34 -0800, Luck, Tony wrote:
> > > All ia64 systems are potentially affected ... but perhaps you might
> > > never see the problem on most because the itc clocks are synced as close
> > > as s/w can get them when cpus are brought on line.
> >
> > Do you want Dimitri to resubmit with this set for all IA64 or leave it
> > as is?
>
> I'd like to understand the impact of turning on HAVE_UNSTABLE_SCHED_CLOCK
>
> It looks like both the i386_defconfig and x86_64_defconfig choose this,
> so at least ia64 will be hitting the well tested code paths
>
> Have the other architectures just not hit this yet? Or do they all have
> "stable" sched_clock() functions?
>
>
> sched_clock() seemed like such a straightforward thing to begin with. A
> quick & easy way to measure a time delta ON THE SAME CPU. I'm not at
> all sure why it has been co-opted for general time measurement.

It came from the complication of needing to tell a remote cpu's time due
to remote wakeups in the scheduler.