RE: Dual core Athlons and unsynced TSCs

john stultz
2006-01-14T01:39:37Z

On Fri, 2006-01-13 at 20:27 -0500, Lee Revell wrote:
> On Fri, 2006-01-13 at 17:23 -0800, john stultz wrote:
> > On Fri, 2006-01-13 at 20:14 -0500, Lee Revell wrote:
> > > On Fri, 2006-01-13 at 20:10 -0500, Steven Rostedt wrote:
> > > >
> > > > Thanks, I'll add that to my list of tests too.
> > > >
> > > > Oh and 2.6.15 passed as well (with clock=pmtmr)
> > >
> > > It really seems like it would fail if you gave it enough time due to the
> > > rdtsc in monotonic_clock()...
> >
> > Currently monotonic_clock()is only used by the hangcheck-timer, and is
> > not used by gettimeofday/clock_gettime (even w/ CLOCK_MONOTONIC).
> >
> > So there may still be an issue there w/ the hangcheck-timer(for x86-64,
> > on i386 the acpi pm timer can be used for monotonic_clock), but its
> > doesn't affect the time related userland interfaces.
>
> OK so the last question is how do we make sure the kernel uses the
> clock=pmtmr behavior by default on those machines?

This is as I understand it:

With 2.6.15 on x86-64:
If available, alternate timesources (HPET, ACPI PM) will be used if
available on AMD SMP systems. (clock= is i386 only)

With 2.6.15 on i386:
If CONFIG_X86_PM_TIMER is enabled, and available it is the preferred
clocksource over the TSC. Some distros have changed this priority
causing the TSC to be preferred. In these cases clock=pmtmr is needed.

How's that?
-john