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SubjectRe: clocksource changes in 2.6.31 - possible regression
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On Mon, 2009-08-17 at 16:02 -0700, Stephen Hemminger wrote:
> On Mon, 17 Aug 2009 15:23:22 -0700
> john stultz <johnstul@us.ibm.com> wrote:
>
> > On Mon, 2009-08-17 at 14:45 -0700, Stephen Hemminger wrote:
> > > On Mon, 17 Aug 2009 14:37:57 -0700
> > > john stultz <johnstul@us.ibm.com> wrote:
> > > > However, I think its fair, that as your TSC is being disqualified for
> > > > being an old AMD SMP box, and there is a *possibility* that if you don't
> > > > run with cpufreq and the SUMA-ness of the box didn't get in the way of
> > > > TSC synchronization, you might have an argument for overriding the
> > > > unsynchronized_tsc() heuristics.
> > > >
> > > > Luckily the option is already there. :)
> > > >
> > > > So try booting with "tsc=reliable" to override those checks, and I think
> > > > you'll be able to do what you want to do.
> > > >
> > >
> > > Good idea, doesn't work.
> > >
> > > vyatta@amd1:~$ cat /proc/cmdline
> > > BOOT_IMAGE=/boot/vmlinuz-2.6.31-rc6 root=/dev/sda1 ro tsc=reliable
> > > vyatta@amd1:~$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> > > acpi_pm
> >
> > Bah! My apologies for half-assing this.
> >
> > How about with the following *tested* patch (includes a variant of
> > Thomas' fix).
> >
> > thanks
> > -john
> >
> >
> > Signed-off-by: John Stultz <johnstul@us.ibm.com>
> >
> > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > index 71f4368..648fb26 100644
> > --- a/arch/x86/kernel/tsc.c
> > +++ b/arch/x86/kernel/tsc.c
> > @@ -825,6 +825,9 @@ __cpuinit int unsynchronized_tsc(void)
> >
> > if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC))
> > return 0;
> > +
> > + if (tsc_clocksource_reliable)
> > + return 0;
> > /*
> > * Intel systems are normally all synchronized.
> > * Exceptions must mark TSC as unstable:
> > @@ -832,10 +835,10 @@ __cpuinit int unsynchronized_tsc(void)
> > if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) {
> > /* assume multi socket systems are not synchronized: */
> > if (num_possible_cpus() > 1)
> > - tsc_unstable = 1;
> > + return 1;
> > }
> >
> > - return tsc_unstable;
> > + return 0;
> > }
> >
> > static void __init init_tsc_clocksource(void)
> >
> >
>
> This adds tsc, but makes it first? it is reliable, but do I want
> to make it most important?
>
> $ cat /sys/devices/system/clocksource/clocksource0/available_clocksource
> tsc acpi_pm


Well, if you're overriding the system saying that its safe, then sure,
its better then anything else, why wouldn't we?

thanks
-john




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