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 X-Spam-Level: X-Spam-Status: No, score=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7DAAC433ED for ; Tue, 4 May 2021 03:09:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BDD1C613AA for ; Tue, 4 May 2021 03:09:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229726AbhEDDJy (ORCPT ); Mon, 3 May 2021 23:09:54 -0400 Received: from mga04.intel.com ([192.55.52.120]:60136 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229687AbhEDDJx (ORCPT ); Mon, 3 May 2021 23:09:53 -0400 IronPort-SDR: pWkFdVKsbeZnY0L9/MQakgXp6K1EGRDu18oqMyCC8mX0gh+9QfMxtOIGbOFcLhMU0D3PD5PRHl NMT97l7pfOxQ== X-IronPort-AV: E=McAfee;i="6200,9189,9973"; a="195832236" X-IronPort-AV: E=Sophos;i="5.82,271,1613462400"; d="scan'208";a="195832236" Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 03 May 2021 20:08:59 -0700 IronPort-SDR: jKpwLl465Zg81mZSn3JwczjUGk3mTvXEOnwrdozZaBGDFqv4z3RCLXk5qcI4NhLOV9A7voYGuX WZS7AVVQ0N8Q== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.82,271,1613462400"; d="scan'208";a="606852163" Received: from ranerica-svr.sc.intel.com ([172.25.110.23]) by orsmga005.jf.intel.com with ESMTP; 03 May 2021 20:08:58 -0700 Date: Mon, 3 May 2021 20:08:14 -0700 From: Ricardo Neri To: Peter Zijlstra Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Len Brown , Srinivas Pandruvada , Tim Chen , Aubrey Li , "Ravi V. Shankar" , Ricardo Neri , Quentin Perret , "Joel Fernandes (Google)" , linux-kernel@vger.kernel.org, Aubrey Li , Ben Segall , Daniel Bristot de Oliveira Subject: Re: [PATCH v2 1/4] sched/fair: Optimize checking for group_asym_packing Message-ID: <20210504030814.GA31635@ranerica-svr.sc.intel.com> References: <20210414020436.12980-1-ricardo.neri-calderon@linux.intel.com> <20210414020436.12980-2-ricardo.neri-calderon@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 03, 2021 at 11:24:25AM +0200, Peter Zijlstra wrote: > On Tue, Apr 13, 2021 at 07:04:33PM -0700, Ricardo Neri wrote: > > By checking local_group, we can avoid additional checks and invoking > > sched_asmy_prefer() when it is not needed. > > This really could do with a few words on *why* that is correct. ISTR > thinking this made sense when I last looked at it, but today, after > having the brain reset by not looking at a computer for 4 days its not > immediate obvious anymore. Thanks for your feedback Peter! I will add a comment explaining why this is correct: when we are collecting statistics of the local group, @env->dst_cpu belongs to @group. @env->dst_cpu may or may not be @group->asym_prefer_cpu. If @env->dst_cpu, sched_asym_prefer() must return false because it would be checking for arch_asym_cpu_priority(dst_cpu) > arch_asym_cpu_priority(dst_cpu) which is false. If @env->dst_cpu is not @group->env_prefer_cpu, it implies that the former has lower prority than the latter and sched_asym_prefer() will also return false. Thanks and BR, Ricardo > > > Signed-off-by: Ricardo Neri > > --- > > kernel/sched/fair.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 04a3ce20da67..4ef3fa0d5e8d 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -8455,7 +8455,7 @@ static inline void update_sg_lb_stats(struct lb_env *env, > > } > > > > /* Check if dst CPU is idle and preferred to this group */ > > - if (env->sd->flags & SD_ASYM_PACKING && > > + if (!local_group && env->sd->flags & SD_ASYM_PACKING && > > env->idle != CPU_NOT_IDLE && > > sgs->sum_h_nr_running && > > sched_asym_prefer(env->dst_cpu, group->asym_prefer_cpu)) { > > -- > > 2.17.1 > >