From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752054AbcDRJRw (ORCPT <rfc822;w@1wt.eu>);
	Mon, 18 Apr 2016 05:17:52 -0400
Received: from LGEAMRELO12.lge.com ([156.147.23.52]:38044 "EHLO
	lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751394AbcDRJRw (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 18 Apr 2016 05:17:52 -0400
X-Original-SENDERIP: 156.147.1.121
X-Original-MAILFROM: byungchul.park@lge.com
X-Original-SENDERIP: 10.177.222.33
X-Original-MAILFROM: byungchul.park@lge.com
Date: Mon, 18 Apr 2016 18:17:21 +0900
From: Byungchul Park <byungchul.park@lge.com>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>, LKML <linux-kernel@vger.kernel.org>,
        Chris Metcalf <cmetcalf@ezchip.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Luiz Capitulino <lcapitulino@redhat.com>,
        Christoph Lameter <cl@linux.com>,
        "Paul E . McKenney" <paulmck@linux.vnet.ibm.com>,
        Mike Galbraith <efault@gmx.de>, Rik van Riel <riel@redhat.com>,
        Ingo Molnar <mingo@elte.hu>
Subject: Re: [PATCH 2/3] sched: Correctly handle nohz ticks cpu load
 accounting
Message-ID: <20160418091721.GH2279@X58A-UD3R>
References: <1460555812-25375-1-git-send-email-fweisbec@gmail.com>
 <1460555812-25375-3-git-send-email-fweisbec@gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1460555812-25375-3-git-send-email-fweisbec@gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

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.