From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E27AC433F5 for ; Fri, 29 Oct 2021 10:01:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 454C861167 for ; Fri, 29 Oct 2021 10:01:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231703AbhJ2KDz (ORCPT ); Fri, 29 Oct 2021 06:03:55 -0400 Received: from foss.arm.com ([217.140.110.172]:36592 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231620AbhJ2KDx (ORCPT ); Fri, 29 Oct 2021 06:03:53 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D8B461063; Fri, 29 Oct 2021 03:01:24 -0700 (PDT) Received: from [192.168.154.184] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 013553F5A1; Fri, 29 Oct 2021 03:01:22 -0700 (PDT) Subject: Re: [PATCH 3/5] sched/fair: Wait before decaying max_newidle_lb_cost To: Vincent Guittot , mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com References: <20211019123537.17146-1-vincent.guittot@linaro.org> <20211019123537.17146-4-vincent.guittot@linaro.org> From: Dietmar Eggemann Message-ID: <67218e25-a472-baa0-19bf-71af26f5e767@arm.com> Date: Fri, 29 Oct 2021 12:01:21 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20211019123537.17146-4-vincent.guittot@linaro.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/10/2021 14:35, Vincent Guittot wrote: > Decay max_newidle_lb_cost only when it has not been updated for a while > and ensure to not decay a recently changed value. > > Signed-off-by: Vincent Guittot > --- > include/linux/sched/topology.h | 2 +- > kernel/sched/fair.c | 36 +++++++++++++++++++++++++--------- > kernel/sched/topology.c | 2 +- > 3 files changed, 29 insertions(+), 11 deletions(-) > > diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h > index 2f9166f6dec8..c07bfa2d80f2 100644 > --- a/include/linux/sched/topology.h > +++ b/include/linux/sched/topology.h > @@ -105,7 +105,7 @@ struct sched_domain { > > /* idle_balance() stats */ > u64 max_newidle_lb_cost; > - unsigned long next_decay_max_lb_cost; > + unsigned long last_decay_max_lb_cost; > > u64 avg_scan_cost; /* select_idle_sibling */ > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index c4c36865321b..e50fd751e1df 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -10239,6 +10239,30 @@ void update_max_interval(void) > max_load_balance_interval = HZ*num_online_cpus()/10; > } > > +static inline bool update_newidle_cost(struct sched_domain *sd, u64 cost) > +{ > + if (cost > sd->max_newidle_lb_cost) { > + /* > + * Track max cost of a domain to make sure to not delay the > + * next wakeup on the CPU. > + */ > + sd->max_newidle_lb_cost = cost; > + sd->last_decay_max_lb_cost = jiffies; That's the actual change of the patch: sd->last_decay_max_lb_cost being moved forward also when newidle cost is updated from newidle_balance() ? > + } else if (time_after(jiffies, sd->last_decay_max_lb_cost + HZ)) { > + /* > + * Decay the newidle max times by ~1% per second to ensure that > + * it is not outdated and the current max cost is actually > + * shorter. I assume that `max cost` refers here to a local variable of the only caller of update_newidle_cost(..., 0) - rebalance_domains()? "the current max cost" has to be shorter so that rq->max_idle_balance_cost also decays in this case. Is this what this comment tries to say here? [...]