Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting

From	Byungchul Park <byungchul.park@lge.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load accounting
Date	2016-04-18 11:20 +0200
Message-ID	<rpdvB-2TT-13@gated-at.bofh.it> (permalink)
References	<rntuO-23t-7@gated-at.bofh.it> <rntuP-23t-39@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Wed, Apr 13, 2016 at 03:56:51PM +0200, Frederic Weisbecker wrote:
> @@ -4645,11 +4674,11 @@ void cpu_load_update_nohz(int active)
>  void cpu_load_update_active(struct rq *this_rq)
>  {
>  	unsigned long load = weighted_cpuload(cpu_of(this_rq));
> -	/*
> -	 * See the mess around cpu_load_update_idle() / cpu_load_update_nohz().
> -	 */
> -	this_rq->last_load_update_tick = jiffies;
> -	__cpu_load_update(this_rq, load, 1, 1);
> +
> +	if (tick_nohz_tick_stopped())
> +		cpu_load_update_nohz(this_rq, READ_ONCE(jiffies), load);
> +	else
> +		cpu_load_update_periodic(this_rq, load);

Considering it further, I wonder if needing it.
(Sorry if I missed something.)

Case 1. tickless -> (scheduler_tick) -> tickless

	I am not sure for this case if the rq's load can be changed or not,
	especially, if the rq's load can be changed *at this point*.
	Please remind that the load[0] is set here.

Case 2. tickless -> (scheduler_tick) -> restart tick

	Will be done by the tick restart routine when exiting irq.
	-> no problem.

Case 3. tick -> (scheduler_tick) -> tickless

	Same as before.
	-> no problem.

Case 4. tick -> (scheduler_tick) -> tick

	We can rely on regular schedule_tick().
	-> no problem.

Back to linux.kernel | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load  accounting Byungchul Park <byungchul.park@lge.com> - 2016-04-18 11:20 +0200
  Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load  accounting Frederic Weisbecker <fweisbec@gmail.com> - 2016-04-18 15:40 +0200
    Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load  accounting Byungchul Park <byungchul.park@lge.com> - 2016-04-19 02:10 +0200
      Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load  accounting Frederic Weisbecker <fweisbec@gmail.com> - 2016-04-19 16:10 +0200

csiph-web