Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754219AbbDNDAT (ORCPT ); Mon, 13 Apr 2015 23:00:19 -0400 Received: from g9t5009.houston.hp.com ([15.240.92.67]:58800 "EHLO g9t5009.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750992AbbDNDAM (ORCPT ); Mon, 13 Apr 2015 23:00:12 -0400 Message-ID: <1428980396.5848.4.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 19:59:56 -0700 In-Reply-To: <1428965360.2605.33.camel@j-VirtualBox> 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> <1428965360.2605.33.camel@j-VirtualBox> 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: 3656 Lines: 124 On Mon, 2015-04-13 at 15:49 -0700, Jason Low wrote: > 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; > } Here's the example patch with the above update. --- diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index ffeaa41..9aa48f7 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7622,6 +7622,16 @@ 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. @@ -7632,9 +7642,13 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) struct rq *rq; int balance_cpu; - if (idle != CPU_IDLE || - !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) - goto end; + if (!test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) + return; + + if (idle != CPU_IDLE) { + pass_nohz_balance(this_rq, this_cpu); + return; + } for_each_cpu(balance_cpu, nohz.idle_cpus_mask) { if (balance_cpu == this_cpu || !idle_cpu(balance_cpu)) @@ -7645,8 +7659,10 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) * work being done for other cpus. Next load * balancing owner will pick it up. */ - if (need_resched()) - break; + if (need_resched()) { + pass_nohz_balance(this_rq, this_cpu); + return; + } rq = cpu_rq(balance_cpu); @@ -7666,7 +7682,6 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) this_rq->next_balance = rq->next_balance; } nohz.next_balance = this_rq->next_balance; -end: clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); } @@ -7689,7 +7704,7 @@ static inline bool nohz_kick_needed(struct rq *rq) int nr_busy, cpu = rq->cpu; bool kick = false; - if (unlikely(rq->idle_balance)) + if (unlikely(idle_cpu(cpu))) return false; /* @@ -7709,7 +7724,7 @@ static inline bool nohz_kick_needed(struct rq *rq) if (time_before(now, nohz.next_balance)) return false; - if (rq->nr_running >= 2) + if (rq->nr_running >= 2 || rq->rd->overload) return true; rcu_read_lock(); @@ -7759,16 +7774,14 @@ static void run_rebalance_domains(struct softirq_action *h) enum cpu_idle_type idle = this_rq->idle_balance ? CPU_IDLE : CPU_NOT_IDLE; + rebalance_domains(this_rq, idle); + /* * If this cpu has a pending nohz_balance_kick, then do the * balancing on behalf of the other idle cpus whose ticks are - * stopped. Do nohz_idle_balance *before* rebalance_domains to - * give the idle cpus a chance to load balance. Else we may - * load balance only within the local sched_domain hierarchy - * and abort nohz_idle_balance altogether if we pull some load. + * stopped. */ nohz_idle_balance(this_rq, idle); - rebalance_domains(this_rq, idle); } /* -- 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/