Re: Interrupt latency on some 945GM platforms

Andi Kleen
2010-09-14T09:55:00Z

Vasily Khoruzhick <anarsoul@gmail.com> writes:

>> Whats the clockevent in this case ("Tick Device" section of
>> /proc/timer_list). clocksource= option only changes the clocksource used
>> to maintain
>> timeofday. But, timer interrupt (clockevent) source will not change.
>> Wondering how just the clocksource change is making the diff here..
>>
>> Also, if clocksource tsc has a higher rating than HPET. The reason
>> HPET is getting used as clocksource in the first place seems to be due
>> to TSC is not a dependable clocksource on this platform (may be it
>> stops in C3). So, I am not sure forcing it to tsc will be a good
>> thing. May be clocksource=acpi_pm is a better thing to try.
>>
>> Thanks,
>> Venki
>
> I investigated it a bit and found out that single nohz=off option helps. Just
> changing clocksource doesn't help, but it works smoothly with any clocksource
> with nohz=off. So, it seems that something wrong with intel driver while
> system is in tickless mode.

It could be simply that nohz=off prevents the system from
going into lower idle states and it is related to that.

You could test this theory by running with processor.max_cstate=1

-Andi

--
ak@linux.intel.com -- Speaking for myself only.