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SubjectRe: [RFC][PATCH 00/32] Nohz cpusets v2 (adaptive tickless kernel)
On Tue, 27 Mar 2012, Peter Zijlstra wrote:

> On Tue, 2012-03-27 at 17:02 +0200, Gilad Ben-Yossef wrote:
> >
> > In my case, I also had to disable the clocksource watchdog, but only
> > because TSC is not stable on my VM.
> > This is really not a nohz/cpuset problem.
>
> No but that thing is annoying, I ran afoul of it too the other day.
>
> Thomas, would you object to a means of turning that thing off? And if
> not, do you have a preference as to what particular means
> (sysctl/sysfs/etc..) ?

We have the commandline option "tsc=reliable" already. That disables
the stupid watchdog. Handle with care.

To take it a level further, use the patch below :)

Thanks,

tglx

------------>
x86: Add tsc=perfect option which enforces sched_clock_stable

The sched_clock dance with updating local clocks can be avoided even
if the CPU does not have all the magic features.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 590900c..dc8ecc3 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -109,6 +109,10 @@ static int __init tsc_setup(char *str)
{
if (!strcmp(str, "reliable"))
tsc_clocksource_reliable = 1;
+ if (!strcmp(str, "perfect")) {
+ tsc_clocksource_reliable = 1;
+ sched_clock_stable = 1;
+ }
if (!strncmp(str, "noirqtime", 9))
no_sched_irq_time = 1;
return 1;


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