Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751768AbbDMWtb (ORCPT ); Mon, 13 Apr 2015 18:49:31 -0400 Received: from g4t3425.houston.hp.com ([15.201.208.53]:34315 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751378AbbDMWta (ORCPT ); Mon, 13 Apr 2015 18:49:30 -0400 Message-ID: <1428965360.2605.33.camel@j-VirtualBox> Subject: Re: sched: Improve load balancing in the presence of idle CPUs From: Jason Low To: Preeti U Murthy Cc: Morten Rasmussen , "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" , jason.low2@hp.com Date: Mon, 13 Apr 2015 15:49:20 -0700 In-Reply-To: <552B5F4F.3030205@linux.vnet.ibm.com> References: <1427741729.5694.24.camel@j-VirtualBox> <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> <552B5F4F.3030205@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: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1841 Lines: 55 > > --- > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index fdae26e..d636bf7 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -7620,6 +7620,16 @@ out: > > } > > > > #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; > > + if (nohz_kick_needed(this_rq)) > > + nohz_balancer_kick(); > > +} > > + > > /* > > * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the > > * rebalancing for all the cpus for whom scheduler ticks are stopped. > > @@ -7631,8 +7641,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) > > int balance_cpu; > > > > if (idle != CPU_IDLE || > > - !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) > > - goto end; > > + !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) { > > + pass_nohz_balance(this_rq, this_cpu); > > + return; > > + } hmm, so taking a look at the patch again, it looks like we pass nohz balance even when the NOHZ_BALANCE_KICK is not set on the current CPU. We should separate the 2 conditions: if (!test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) return; if (idle != CPU_IDLE) { /* another CPU continue balancing */ pass_nohz_balance(this_rq, this_cpu); return; } In general, separating the check also optimizes nohz_idle_balance() to avoid clearing the bit when it is not set. -- 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/