Re: System tick rate

[Peter Zijlstra]

On Thu, 2009-03-12 at 15:45 +0100, Jan Engelhardt wrote:
> On Thursday 2009-03-12 15:21, Arjan van de Ven wrote:
> >On Thu, 12 Mar 2009 14:38:19 +0100 (CET) Jan Engelhardt wrote:
> >> 
> >> is there an "official" way of obtaining the current tick rate when 
> >> CONFIG_NO_HZ? 
> >
> >what does "current tick rate" mean for you in a no-hz situation ?
> >is it the HZ value (which is supposed to be invisible from userspace,
> >so good luck) or the wakeup count ?
> 
> Hm, I guess what I want is the number of timer interrupts which
> occurred within the observation period that called the scheduler
> code. (So that excludes RTC on usual x86en.)

There is no tick rate with NO_HZ mode, only a max tick rate, but as
Arjan said, not even that is exposed to user-space.

I think Dave's Niagra has the crown here, because he ran into some bug
in the NO_HZ code some while back because he idled longer than we ever
seen before. I think it was in the order of 30 minutes or something
without a single wakeup of the CPU.




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