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

From: Peter Zijlstra <peterz@infradead.org>
To: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: rjw@rjwysocki.net, preeti@linux.vnet.ibm.com,
	nicolas.pitre@linaro.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org,
	patches@linaro.org, lenb@kernel.org
Subject: Re: [PATCH V3 3/6] sched: idle: Get the next timer event and pass it the cpuidle framework
Date: Mon, 10 Nov 2014 13:43:53 +0100	[thread overview]
Message-ID: <20141110124353.GO3337@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1415370687-18688-4-git-send-email-daniel.lezcano@linaro.org>

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.