Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932190AbbDJIil (ORCPT ); Fri, 10 Apr 2015 04:38:41 -0400 Received: from e28smtp07.in.ibm.com ([122.248.162.7]:34812 "EHLO e28smtp07.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754341AbbDJIiT (ORCPT ); Fri, 10 Apr 2015 04:38:19 -0400 Date: Fri, 10 Apr 2015 14:07:41 +0530 From: Srikar Dronamraju To: Jason Low Cc: Preeti U Murthy , Morten Rasmussen , "peterz@infradead.org" , "mingo@kernel.org" , Daniel Lezcano , "riel@redhat.com" , "vincent.guittot@linaro.org" , "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" Subject: Re: sched: Improve load balancing in the presence of idle CPUs Message-ID: <20150410083741.GB10331@linux.vnet.ibm.com> Reply-To: Srikar Dronamraju References: <551A5CCE.70008@linux.vnet.ibm.com> <1427828056.2492.24.camel@j-VirtualBox> <551B9514.80701@linux.vnet.ibm.com> <20150401170418.GX18994@e105550-lin.cambridge.arm.com> <1427954347.2556.43.camel@j-VirtualBox> <551FB5F5.5050906@linux.vnet.ibm.com> <1428449300.2556.79.camel@j-VirtualBox> <1428451666.2556.84.camel@j-VirtualBox> <20150408111216.GA24645@linux.vnet.ibm.com> <1428528169.3506.34.camel@j-VirtualBox> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <1428528169.3506.34.camel@j-VirtualBox> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15041008-0025-0000-0000-0000043016E6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1285 Lines: 41 > > > > > > #ifdef CONFIG_NO_HZ_COMMON > > > +static inline bool nohz_kick_needed(struct rq *rq); > > > + > > > +static inline void pass_nohz_balance(struct rq *this_rq, int this_cpu) > > > +{ > > > + clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); > > > + nohz.next_balance = jiffies; > > > > Why are we updating nohz.next_balance here? > > This was just to make sure that since we're continuing the balancing on > another CPU that the nohz next_balance is guaranteed to be "now". > Since we are in nohz_idle_balance(), nohz.next_balance is guaranteed be less than now. We do check for time_before(now, nohz.next_balance) in nohz_kick_needed(). So in effect we are incrementing the nohz.next_balance. While updating nohz.next_balance may not cause any issues, it atleast look redundant to me. At this point, I also wanted to understand why we do "nohz.next_balance++" nohz_balancer_kick()? > > > + if (nohz_kick_needed(this_rq)) > > > + nohz_balancer_kick(); > > > +} > > > + > > > /* -- Thanks and Regards Srikar Dronamraju -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/