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

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Message-ID: <5460D6A6.9070501@linaro.org>
Date:	Mon, 10 Nov 2014 16:15:50 +0100
From:	Daniel Lezcano <daniel.lezcano@...aro.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	rjw@...ysocki.net, preeti@...ux.vnet.ibm.com,
	nicolas.pitre@...aro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-kernel@...ts.linaro.org,
	patches@...aro.org, lenb@...nel.org
Subject: Re: [PATCH V3 3/6] sched: idle: Get the next timer event and pass
 it the cpuidle framework

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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