Re: [QUERY]: Is using CPU hotplug right for isolating CPUs?

From: Viresh Kumar
Date: Tue Jan 21 2014 - 05:34:04 EST

On 20 January 2014 21:21, Frederic Weisbecker <fweisbec@xxxxxxxxx> wrote:
> I fear you can't. If you schedule a timer in 4 seconds away and your clockdevice
> can only count up to 2 seconds, you can't help much the interrupt in the middle to
> cope with the overflow.
> So you need to act on the source of the timer:
> * identify what cause this timer
> * try to turn that feature off
> * if you can't then move the timer to the housekeeping CPU

So, the main problem in my case was caused by this:

<...>-2147 [001] d..2 302.573881: hrtimer_start:
hrtimer=c172aa50 function=tick_sched_timer expires=602075000000

I have mentioned this earlier when I sent you attachments. I think
this is somehow
tied with the NO_HZ_FULL stuff? As the timer is queued for 300 seconds after
current time.

How to get this out?

> I'll have a look into the latter point to affine global timers to the
> housekeeping CPU. Per cpu timers need more inspection though. Either we rework
> them to be possibly handled by remote/housekeeping CPUs, or we let the associate feature
> to be turned off. All in one it's a case by case work.

Which CPUs are housekeeping CPUs? How do we declare them?
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