Re: [ANNOUNCE] 4.4-rc6-rt1

[Thomas Gleixner]

On Thu, 14 Jan 2016, Mike Galbraith wrote:

> On Thu, 2016-01-14 at 15:17 +0100, Sebastian Andrzej Siewior wrote:
> > * Sebastian Andrzej Siewior | 2016-01-13 18:58:45 [+0100]:
> > 
> > > This is due to NO_HZ as far as I can tell. My AMD A10 in idle mode
> > > has
> > > 0.7% utilisation of ksoftirqd/ with CONFIG_HZ_PERIODIC and with
> > > CONFIG_NO_HZ_FULL it shows about 25% on all CPU threads.
> > 
> > This should fixed it:
> > 
> > --- a/kernel/time/timer.c
> > +++ b/kernel/time/timer.c
> > @@ -1453,7 +1453,7 @@ u64 get_next_timer_interrupt(unsigned long
> > basej, u64 basem)
> >  	 * the base lock to check when the next timer is pending and
> > so
> >  	 * we assume the next jiffy.
> >  	 */
> > -	return basej;
> > +	return basem + TICK_NSEC;
> >  #endif
> >  	spin_lock(&base->lock);
> >  	if (base->active_timers) {
> 
> That's what I had done to stop the screaming interrupt, but box still
> behaved very badly.

If you turn off CONFIG_NO_HZ_FULL and switch to NO_HZ_IDLE is it still bad?

Thanks,

	tglx