Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752683AbbDBGAl (ORCPT ); Thu, 2 Apr 2015 02:00:41 -0400 Received: from g2t2352.austin.hp.com ([15.217.128.51]:43368 "EHLO g2t2352.austin.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751255AbbDBGAk (ORCPT ); Thu, 2 Apr 2015 02:00:40 -0400 Message-ID: <1427954347.2556.43.camel@j-VirtualBox> Subject: Re: sched: Improve load balancing in the presence of idle CPUs From: Jason Low To: Morten Rasmussen Cc: Preeti U Murthy , "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: Wed, 01 Apr 2015 22:59:07 -0700 In-Reply-To: <20150401170418.GX18994@e105550-lin.cambridge.arm.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> 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: 3214 Lines: 100 On Wed, 2015-04-01 at 18:04 +0100, Morten Rasmussen wrote: > On Wed, Apr 01, 2015 at 07:49:56AM +0100, Preeti U Murthy wrote: > > I am sorry I don't quite get this. Can you please elaborate? > > I think the scenario is that we are in nohz_idle_balance() and decide to > bail out because we have pulled some tasks, but before leaving > nohz_idle_balance() we want to check if more balancing is necessary > using nohz_kick_needed() and potentially kick somebody to continue. Also, below is an example patch. (Without the conversion to idle_cpu(), the check for rq->idle_balance would not be accurate anymore) --- kernel/sched/fair.c | 17 ++++++++++------- 1 files changed, 10 insertions(+), 7 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index fdae26e..7749a14 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7620,6 +7620,8 @@ out: } #ifdef CONFIG_NO_HZ_COMMON +static inline bool nohz_kick_needed(struct rq *rq); + /* * In CONFIG_NO_HZ_COMMON case, the idle balance kickee will do the * rebalancing for all the cpus for whom scheduler ticks are stopped. @@ -7629,6 +7631,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) int this_cpu = this_rq->cpu; struct rq *rq; int balance_cpu; + bool done_balancing = false; if (idle != CPU_IDLE || !test_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu))) @@ -7644,7 +7647,7 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) * balancing owner will pick it up. */ if (need_resched()) - break; + goto end; rq = cpu_rq(balance_cpu); @@ -7663,9 +7666,12 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) if (time_after(this_rq->next_balance, rq->next_balance)) this_rq->next_balance = rq->next_balance; } + done_balancing = true; nohz.next_balance = this_rq->next_balance; end: clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); + if (!done_balancing && nohz_kick_needed(this_rq)) + nohz_balancer_kick(); } /* @@ -7687,7 +7693,7 @@ 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; /* @@ -7757,16 +7763,13 @@ 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); } /* -- 1.7.2.5 -- 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/