Re: [PATCH] Reduce cacheline bouncing in cpu_idle_wait

[Zwane Mwaikambo]

On Thu, 10 Mar 2005, Andi Kleen wrote:

> Zwane Mwaikambo <zwane@xxxxxxxxxxxxxxxx> writes:
> 
> > Andi noted that during normal runtime cpu_idle_map is bounced around a 
> > lot, and occassionally at a higher frequency than the timer interrupt 
> > wakeup which we normally exit pm_idle from. So switch to a percpu 
> > variable. Andi i didn't move things to the slow path because it would 
> > involve adding scheduler code to wakeup the idle thread on the cpus we're 
> > waiting for.
> 
> Thanks. 
> >  
> > -
> >  void cpu_idle_wait(void)
> >  {
> > -        int cpu;
> > -        cpumask_t map;
> > +	unsigned int cpu, this_cpu = get_cpu();
> > +	cpumask_t map;
> > +
> > +	set_cpus_allowed(current, cpumask_of_cpu(this_cpu));
> > +	put_cpu();
> 
> You need a cpus_clear(map); here I think (probably same for the other
> archs) 

A bit subtle, the cpus_and will clear the offline processors after the 
first pass.
-
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