From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752189AbbDAGuL (ORCPT ); Wed, 1 Apr 2015 02:50:11 -0400 Received: from e31.co.us.ibm.com ([32.97.110.149]:55873 "EHLO e31.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751138AbbDAGuJ (ORCPT ); Wed, 1 Apr 2015 02:50:09 -0400 Message-ID: <551B9514.80701@linux.vnet.ibm.com> Date: Wed, 01 Apr 2015 12:19:56 +0530 From: Preeti U Murthy User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 MIME-Version: 1.0 To: Jason Low CC: peterz@infradead.org, mingo@kernel.org, Daniel Lezcano , 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 Subject: Re: sched: Improve load balancing in the presence of idle CPUs References: <1427741729.5694.24.camel@j-VirtualBox> <551A5CCE.70008@linux.vnet.ibm.com> <1427828056.2492.24.camel@j-VirtualBox> In-Reply-To: <1427828056.2492.24.camel@j-VirtualBox> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15040106-8236-0000-0000-00000A7D55AB Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/01/2015 12:24 AM, Jason Low wrote: > 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 potentially outdated value to be used if this cpu is able to pull tasks 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? I am sorry I don't quite get this. Can you please elaborate? Regards Preeti U Murthy >