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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 B731CC83003 for ; Wed, 29 Apr 2020 12:01:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 91F532083B for ; Wed, 29 Apr 2020 12:01:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726817AbgD2MBG (ORCPT ); Wed, 29 Apr 2020 08:01:06 -0400 Received: from foss.arm.com ([217.140.110.172]:37838 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726426AbgD2MBG (ORCPT ); Wed, 29 Apr 2020 08:01:06 -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 CCB321063; Wed, 29 Apr 2020 05:01:05 -0700 (PDT) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7B6583F73D; Wed, 29 Apr 2020 05:01:04 -0700 (PDT) References: <20200428050242.17717-1-swood@redhat.com> <20200428050242.17717-2-swood@redhat.com> <2a30101cc0adb63ee7ce7b32119579d78de24b71.camel@redhat.com> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Scott Wood Cc: Steven Rostedt , Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Rik van Riel , Mel Gorman , linux-kernel@vger.kernel.org, linux-rt-users Subject: Re: [RFC PATCH 1/3] sched/fair: Call newidle_balance() from finish_task_switch() Message-ID: In-reply-to: <2a30101cc0adb63ee7ce7b32119579d78de24b71.camel@redhat.com> Date: Wed, 29 Apr 2020 13:00:58 +0100 MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/04/20 23:33, Scott Wood wrote: > On Tue, 2020-04-28 at 22:37 +0100, Valentin Schneider wrote: >> On 28/04/20 06:02, Scott Wood wrote: >> > Thus, newidle_balance() is entered with interrupts enabled, which allows >> > (in the next patch) enabling interrupts when the lock is dropped. >> > >> > Signed-off-by: Scott Wood >> > --- >> > kernel/sched/core.c | 7 ++++--- >> > kernel/sched/fair.c | 45 ++++++++++++++++---------------------------- >> > kernel/sched/sched.h | 6 ++---- >> > 3 files changed, 22 insertions(+), 36 deletions(-) >> > >> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> > index 9a2fbf98fd6f..0294beb8d16c 100644 >> > --- a/kernel/sched/core.c >> > +++ b/kernel/sched/core.c >> > @@ -3241,6 +3241,10 @@ static struct rq *finish_task_switch(struct >> > task_struct *prev) >> > } >> > >> > tick_nohz_task_switch(); >> > + >> > + if (is_idle_task(current)) >> > + newidle_balance(); >> > + >> >> This means we must go through a switch_to(idle) before figuring out we >> could've switched to a CFS task, and do it then. I'm curious to see the >> performance impact of that. > > Any particular benchmark I should try? > I'm going to be very original and suggest hackbench :-) That would just be the first stop however, you would also want to try something less wakeup-intensive, maybe sysbench and the like - I'm thinking if you spawn ~1.5*nr_cpu_ids CPU-hogs, you'll hit that double switch fairly easily. And then there's always the big boys benchmarks like specjbb and co - I'd suggest having a look at Mel's mmtests.