Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752428AbbDCWfV (ORCPT ); Fri, 3 Apr 2015 18:35:21 -0400 Received: from mga02.intel.com ([134.134.136.20]:21543 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752057AbbDCWfT (ORCPT ); Fri, 3 Apr 2015 18:35:19 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,520,1422950400"; d="scan'208";a="708633662" Message-ID: <1428100518.660.34.camel@schen9-desk2.jf.intel.com> Subject: Re: sched: Improve load balancing in the presence of idle CPUs From: Tim Chen To: Jason Low Cc: Morten Rasmussen , 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" Date: Fri, 03 Apr 2015 15:35:18 -0700 In-Reply-To: <1427954347.2556.43.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> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.5 (3.8.5-2.fc19) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3423 Lines: 96 On Wed, 2015-04-01 at 22:59 -0700, Jason Low wrote: > 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(); > } > > I think we can get rid of the done_balancing boolean and make it a bit easier to read if we change the above code to diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index bcfe320..08317dc 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7557,8 +7557,13 @@ 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()) { + /* preparing to bail, kicking other cpu to continue */ + clear_bit(NOHZ_BALANCE_KICK, nohz_flags(this_cpu)); + if (nohz_kick_needed(this_rq)) + nohz_balance_kick(); + return; + } rq = cpu_rq(balance_cpu); Thanks. Tim -- 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/