From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754107AbdBNPif (ORCPT ); Tue, 14 Feb 2017 10:38:35 -0500 Received: from mail-lf0-f66.google.com ([209.85.215.66]:34120 "EHLO mail-lf0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682AbdBNPi0 (ORCPT ); Tue, 14 Feb 2017 10:38:26 -0500 From: Uladzislau Rezki To: Peter Zijlstra Cc: LKML , Ingo Molnar , Mike Galbraith , Oleksiy Avramchenko , Uladzislau 2 Rezki Subject: [PATCH] sched: ignore task_h_load for CPU_NEWLY_IDLE Date: Tue, 14 Feb 2017 16:38:05 +0100 Message-Id: <1487086685-7585-1-git-send-email-urezki@gmail.com> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Uladzislau 2 Rezki A load balancer calculates imbalance factor for particular sched domain and tries to steal up the prescribed amount of weighted load. However, a small imbalance factor would sometimes prevent us from stealing any tasks at all. When a CPU is newly idle, it should steal first task which meets the migration criteria. There is a slight improvement when it comes to frame drops (in my case drops per/two seconds). Basically a test case is left finger swipe on the display (21 times, duration is 2 seconds + 1 second sleep between iterations): 0 Framedrops: 7 5 1 Framedrops: 5 3 2 Framedrops: 8 5 3 Framedrops: 4 5 4 Framedrops: 3 3 5 Framedrops: 6 4 6 Framedrops: 3 2 7 Framedrops: 3 4 8 Framedrops: 5 3 9 Framedrops: 3 3 10 Framedrops: 7 4 11 Framedrops: 3 4 12 Framedrops: 3 3 13 Framedrops: 3 3 14 Framedrops: 3 5 15 Framedrops: 7 3 16 Framedrops: 5 3 17 Framedrops: 3 2 18 Framedrops: 5 3 19 Framedrops: 4 3 20 Framedrops: 3 2 max is 8 vs 5; min is 3 vs 2. As for applied load, it is not significant and is "light". Signed-off-by: Uladzislau 2 Rezki --- kernel/sched/fair.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 6559d19..b56b0c5 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6802,6 +6802,15 @@ static int detach_tasks(struct lb_env *env) if (env->idle != CPU_NOT_IDLE && env->src_rq->nr_running <= 1) break; + /* + * Another CPU can place tasks, since we do not hold dst_rq lock + * while doing balancing. If newly idle CPU already got something, + * give up to reduce latency for CONFIG_PREEMPT kernels. + */ + if (IS_ENABLED(CONFIG_PREEMPT) && env->idle == CPU_NEWLY_IDLE && + env->dst_rq->nr_running > 0) + break; + p = list_first_entry(tasks, struct task_struct, se.group_node); env->loop++; @@ -6824,7 +6833,8 @@ static int detach_tasks(struct lb_env *env) if (sched_feat(LB_MIN) && load < 16 && !env->sd->nr_balance_failed) goto next; - if ((load / 2) > env->imbalance) + if ((!IS_ENABLED(CONFIG_PREEMPT) || env->idle != CPU_NEWLY_IDLE) && + (load / 2) > env->imbalance) goto next; detach_task(p, env); -- 2.1.4