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

Daniel Lezcano
2014-11-10T15:15:58Z

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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