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 S1752639AbbCaSyV (ORCPT <rfc822;w@1wt.eu>);
	Tue, 31 Mar 2015 14:54:21 -0400
Received: from g4t3425.houston.hp.com ([15.201.208.53]:2266 "EHLO
	g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751138AbbCaSyT (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Tue, 31 Mar 2015 14:54:19 -0400
Message-ID: <1427828056.2492.24.camel@j-VirtualBox>
Subject: Re: sched: Improve load balancing in the presence of idle CPUs
From: Jason Low <jason.low2@hp.com>
To: Preeti U Murthy <preeti@linux.vnet.ibm.com>
Cc: peterz@infradead.org, mingo@kernel.org,
        Daniel Lezcano <daniel.lezcano@linaro.org>, riel@redhat.com,
        vincent.guittot@linaro.org, srikar@linux.vnet.ibm.com, pjt@google.com,
        benh@kernel.crashing.org, efault@gmx.de, linux-kernel@vger.kernel.org,
        iamjoonsoo.kim@lge.com, svaidy@linux.vnet.ibm.com,
        tim.c.chen@linux.intel.com, morten.rasmussen@arm.com,
        jason.low2@hp.com
Date: Tue, 31 Mar 2015 11:54:16 -0700
In-Reply-To: <551A5CCE.70008@linux.vnet.ibm.com>
References: <1427741729.5694.24.camel@j-VirtualBox>
	 <551A5CCE.70008@linux.vnet.ibm.com>
Content-Type: text/plain; charset="UTF-8"
X-Mailer: Evolution 3.2.3-0ubuntu6 
Content-Transfer-Encoding: 7bit
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, 2015-03-31 at 14:07 +0530, Preeti U Murthy wrote:
> Hi Jason,
> 
> On 03/31/2015 12:25 AM, Jason Low wrote:
> > Hi Preeti,
> > 
> > I noticed that another commit 4a725627f21d converted the check in
> > nohz_kick_needed() from idle_cpu() to rq->idle_balance, causing a
> > potentially outdated value to be used if this cpu is able to pull tasks
> > using rebalance_domains(), and nohz_kick_needed() directly returning
> > false.
> 
> I see that rebalance_domains() will be run at the end of the scheduler
> tick interrupt handling. trigger_load_balance() only sets the softirq,
> it does not call rebalance_domains() immediately. So the call graph
> would be:

Oh right, since that only sets the softirq, this wouldn't be the issue,
though we would need these changes if we were to incorporate any sort of
nohz_kick_needed() logic into the nohz_idle_balance() code path correct?