Re: clocksource changes in 2.6.31 - possible regression

From: john stultz
Date: Mon Aug 17 2009 - 18:24:37 EST


On Mon, 2009-08-17 at 14:45 -0700, Stephen Hemminger wrote:
> On Mon, 17 Aug 2009 14:37:57 -0700
> john stultz <johnstul@xxxxxxxxxx> 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@xxxxxxxxxx>

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)


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