Re: [PATCH V3 3/6] sched: idle: Get the next timer event and pass it the cpuidle framework

[Daniel Lezcano]

On 11/10/2014 01:43 PM, Peter Zijlstra wrote:
> On Fri, Nov 07, 2014 at 03:31:24PM +0100, Daniel Lezcano wrote:
> >   static void cpu_idle_loop(void)
> >   {
> > -	unsigned int latency_req;
> > +	unsigned int latency_req, next_timer_event;
> >
> >   	while (1) {
> >   		/*
> > @@ -221,6 +222,9 @@ static void cpu_idle_loop(void)
> >
> >   			latency_req = pm_qos_request(PM_QOS_CPU_DMA_LATENCY);
> >
> > +			next_timer_event =
> > +				ktime_to_us(tick_nohz_get_sleep_length());
> > +
> >   			/*
> >   			 * In poll mode we reenable interrupts and spin.
> >   			 *
> > @@ -238,7 +242,8 @@ static void cpu_idle_loop(void)
> >   			    tick_check_broadcast_expired())
> >   				cpu_idle_poll();
> >   			else
> > -				cpuidle_idle_call(latency_req);
> > +				cpuidle_idle_call(latency_req,
> > +						  next_timer_event);
> >
> >   			arch_cpu_idle_exit();
> >   		}
>
> Why do we want to query the next timer in the poll case? Afaict the
> other patches don't make use of this either.

Well, the direction I am taking when writing those cleanups is to have 
something like:

"I will sleep X usec, I have Y usec latency constraints". Grouping the 
latency req and the next timer allows to stick to the next changes.


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