Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752866AbaDXBcR (ORCPT ); Wed, 23 Apr 2014 21:32:17 -0400 Received: from g9t1613g.houston.hp.com ([15.240.0.71]:45298 "EHLO g9t1613g.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752446AbaDXBba (ORCPT ); Wed, 23 Apr 2014 21:31:30 -0400 From: Jason Low To: mingo@kernel.org, peterz@infradead.org, jason.low2@hp.com Cc: linux-kernel@vger.kernel.org, daniel.lezcano@linaro.org, alex.shi@linaro.org, preeti@linux.vnet.ibm.com, efault@gmx.de, vincent.guittot@linaro.org, morten.rasmussen@arm.com, aswin@hp.com, chegu_vinod@hp.com Subject: [PATCH 3/3] sched, fair: Stop searching for tasks in newidle balance if there are runnable tasks Date: Wed, 23 Apr 2014 18:30:35 -0700 Message-Id: <1398303035-18255-4-git-send-email-jason.low2@hp.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1398303035-18255-1-git-send-email-jason.low2@hp.com> References: <1398303035-18255-1-git-send-email-jason.low2@hp.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It was found that when running some workloads (such as AIM7) on large systems with many cores, CPUs do not remain idle for long. Thus, tasks can wake/get enqueued while doing idle balancing. In this patch, while traversing the domains in idle balance, in addition to checking for pulled_task, we add an extra check for this_rq->nr_running for determining if we should stop searching for tasks to pull. If there are runnable tasks on this rq, then we will stop traversing the domains. This reduces the chance that idle balance delays a task from running. This patch resulted in approximately a 6% performance improvement when running a Java Server workload on an 8 socket machine. Signed-off-by: Jason Low --- kernel/sched/fair.c | 8 ++++++-- 1 files changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3e3ffb8..232518c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6689,7 +6689,6 @@ static int idle_balance(struct rq *this_rq) if (sd->flags & SD_BALANCE_NEWIDLE) { t0 = sched_clock_cpu(this_cpu); - /* If we've pulled tasks over stop searching: */ pulled_task = load_balance(this_cpu, this_rq, sd, CPU_NEWLY_IDLE, &continue_balancing); @@ -6704,7 +6703,12 @@ static int idle_balance(struct rq *this_rq) interval = msecs_to_jiffies(sd->balance_interval); if (time_after(next_balance, sd->last_balance + interval)) next_balance = sd->last_balance + interval; - if (pulled_task) + + /* + * Stop searching for tasks to pull if there are + * now runnable tasks on this rq. + */ + if (pulled_task || this_rq->nr_running > 0) break; } rcu_read_unlock(); -- 1.7.1 -- 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/