From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750897AbaETURl (ORCPT ); Tue, 20 May 2014 16:17:41 -0400 Received: from mga09.intel.com ([134.134.136.24]:33470 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750755AbaETURk (ORCPT ); Tue, 20 May 2014 16:17:40 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.98,875,1392192000"; d="scan'208";a="543815942" Subject: [PATCH] sched: Reduce the rate of needless idle load balancing From: Tim Chen To: Ingo Molnar , Peter Zijlstra Cc: Andrew Morton , Len Brown , Russ Anderson , Dimitri Sivanich , Hedi Berriche , Andi Kleen , Michel Lespinasse , Rik van Riel , Peter Hurley , linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Date: Tue, 20 May 2014 13:17:26 -0700 Message-ID: <1400617046.2970.270.camel@schen9-DESK> Mime-Version: 1.0 X-Mailer: Evolution 2.32.3 (2.32.3-1.fc14) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The current no_hz idle load balancer do load balancing on *all* idle cpus, even though the time due to load balance for a particular idle cpu could be still a while in future. This introduces a much higher load balancing rate than what is necessary. The patch changes the behavior by only doing idle load balancing on behalf of an idle cpu only when time is due for load balancing. On SGI's systems with over 3000 cores, the cpu responsible for idle balancing got overwhelmed with idle balancing, and introduces a lot of OS noise to workloads. This patch fixes the issue. Thanks. Tim Acked-by: Russ Anderson Signed-off-by: Tim Chen --- kernel/sched/fair.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 9b4c4f3..97132db 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6764,12 +6764,17 @@ static void nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle) rq = cpu_rq(balance_cpu); - raw_spin_lock_irq(&rq->lock); - update_rq_clock(rq); - update_idle_cpu_load(rq); - raw_spin_unlock_irq(&rq->lock); - - rebalance_domains(rq, CPU_IDLE); + /* + * If time for next balance is due, + * do the balance. + */ + if (time_after(jiffies + 1, rq->next_balance)) { + raw_spin_lock_irq(&rq->lock); + update_rq_clock(rq); + update_idle_cpu_load(rq); + raw_spin_unlock_irq(&rq->lock); + rebalance_domains(rq, CPU_IDLE); + } if (time_after(this_rq->next_balance, rq->next_balance)) this_rq->next_balance = rq->next_balance; -- 1.7.11.7