From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752629AbeFDL66 (ORCPT ); Mon, 4 Jun 2018 07:58:58 -0400 Received: from foss.arm.com ([217.140.101.70]:42226 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751473AbeFDL64 (ORCPT ); Mon, 4 Jun 2018 07:58:56 -0400 From: Quentin Perret To: peterz@infradead.org, mingo@redhat.com Cc: linux-kernel@vger.kernel.org, yuyang.du@intel.com, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, patrick.bellasi@arm.com, vincent.guittot@linaro.org, Quentin Perret Subject: [PATCH] sched/fair: Fix util_avg of new tasks for asymmetric systems Date: Mon, 4 Jun 2018 12:58:30 +0100 Message-Id: <20180604115830.18781-1-quentin.perret@arm.com> X-Mailer: git-send-email 2.17.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When a new task wakes-up for the first time, its initial utilization is set to half of the spare capacity of its CPU. The current implementation of post_init_entity_util_avg() uses SCHED_CAPACITY_SCALE directly as a capacity reference. As a result, on a big.LITTLE system, a new task waking up on an idle little CPU will be given ~512 of util_avg, even if the CPU's capacity is significantly less than that. Fix this by computing the spare capacity with arch_scale_cpu_capacity(). Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Quentin Perret --- kernel/sched/fair.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index e497c05aab7f..f19432c17017 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -735,11 +735,12 @@ static void attach_entity_cfs_rq(struct sched_entity *se); * To solve this problem, we also cap the util_avg of successive tasks to * only 1/2 of the left utilization budget: * - * util_avg_cap = (1024 - cfs_rq->avg.util_avg) / 2^n + * util_avg_cap = (cpu_scale - cfs_rq->avg.util_avg) / 2^n * - * where n denotes the nth task. + * where n denotes the nth task and cpu_scale the CPU capacity. * - * For example, a simplest series from the beginning would be like: + * For example, for a CPU with 1024 of capacity, a simplest series from + * the beginning would be like: * * task util_avg: 512, 256, 128, 64, 32, 16, 8, ... * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ... @@ -751,7 +752,8 @@ void post_init_entity_util_avg(struct sched_entity *se) { struct cfs_rq *cfs_rq = cfs_rq_of(se); struct sched_avg *sa = &se->avg; - long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2; + long cpu_scale = arch_scale_cpu_capacity(NULL, cpu_of(rq_of(cfs_rq))); + long cap = (long)(cpu_scale - cfs_rq->avg.util_avg) / 2; if (cap > 0) { if (cfs_rq->avg.util_avg != 0) { -- 2.17.0