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=-6.6 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 54D9AC433E3 for ; Wed, 19 Aug 2020 11:56:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A43C2072D for ; Wed, 19 Aug 2020 11:56:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728179AbgHSL4H (ORCPT ); Wed, 19 Aug 2020 07:56:07 -0400 Received: from foss.arm.com ([217.140.110.172]:34086 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728301AbgHSLzx (ORCPT ); Wed, 19 Aug 2020 07:55:53 -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 F04E61063; Wed, 19 Aug 2020 04:55:50 -0700 (PDT) Received: from [192.168.178.2] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 79F253F71F; Wed, 19 Aug 2020 04:55:49 -0700 (PDT) Subject: Re: [PATCH] sched/fair: reduce preemption with IDLE tasks runable(Internet mail) To: Vincent Guittot Cc: =?UTF-8?B?YmVuYmppYW5nKOiSi+W9qik=?= , Jiang Biao , "mingo@redhat.com" , "peterz@infradead.org" , "juri.lelli@redhat.com" , "rostedt@goodmis.org" , "bsegall@google.com" , "mgorman@suse.de" , "linux-kernel@vger.kernel.org" References: <20200801023248.90104-1-benbjiang@gmail.com> <5ed0fd46-3a3d-3c1a-5d75-03a74864e640@arm.com> <592F24A7-BF43-457D-AC40-DC5E35279730@tencent.com> <8bef1f94-f9bf-08a5-2ff3-3485d7796a96@arm.com> <8629CB9F-AFC8-43D6-BD14-B60A0B85ADB3@tencent.com> <5f870781-1648-b4ac-6026-557dfc347109@arm.com> <4964e359-afc5-a256-4950-853a9485eeff@arm.com> <70236E62-AA36-48C1-9382-86353649253C@tencent.com> <3a1047fc-a86a-014a-b17a-eae71f669da1@arm.com> <643B0ECE-D758-4D08-8B1B-C70F34DD9943@tencent.com> <55f04582-69d6-aeb4-85be-3e46a3b15beb@arm.com> <755BFAD0-9072-4D73-9CD7-AF4F74A79D21@tencent.com> <729675a2-b083-4211-62c0-f7ed7f483ae2@arm.com> From: Dietmar Eggemann Message-ID: Date: Wed, 19 Aug 2020 13:55:44 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/08/2020 13:05, Vincent Guittot wrote: > On Wed, 19 Aug 2020 at 12:46, Dietmar Eggemann wrote: >> >> On 17/08/2020 14:05, benbjiang(蒋彪) wrote: >>> >>> >>>> On Aug 17, 2020, at 4:57 PM, Dietmar Eggemann wrote: >>>> >>>> On 14/08/2020 01:55, benbjiang(蒋彪) wrote: >>>>> Hi, >>>>> >>>>>> On Aug 13, 2020, at 2:39 AM, Dietmar Eggemann wrote: >>>>>> >>>>>> On 12/08/2020 05:19, benbjiang(蒋彪) wrote: >>>>>>> Hi, >>>>>>> >>>>>>>> On Aug 11, 2020, at 11:54 PM, Dietmar Eggemann wrote: >>>>>>>> >>>>>>>> On 11/08/2020 02:41, benbjiang(蒋彪) wrote: >>>>>>>>> Hi, >>>>>>>>> >>>>>>>>>> On Aug 10, 2020, at 9:24 PM, Dietmar Eggemann wrote: >>>>>>>>>> >>>>>>>>>> On 06/08/2020 17:52, benbjiang(蒋彪) wrote: >>>>>>>>>>> Hi, >>>>>>>>>>> >>>>>>>>>>>> On Aug 6, 2020, at 9:29 PM, Dietmar Eggemann wrote: >>>>>>>>>>>> >>>>>>>>>>>> On 03/08/2020 13:26, benbjiang(蒋彪) wrote: >>>>>>>>>>>>> >>>>>>>>>>>>> >>>>>>>>>>>>>> On Aug 3, 2020, at 4:16 PM, Dietmar Eggemann wrote: >>>>>>>>>>>>>> >>>>>>>>>>>>>> On 01/08/2020 04:32, Jiang Biao wrote: >>>>>>>>>>>>>>> From: Jiang Biao >> >> [...] >> >>>> Are you sure about this? >>> Yes. :) >>>> >>>> The math is telling me for the: >>>> >>>> idle task: (3 / (1024 + 1024 + 3))^(-1) * 4ms = 2735ms >>>> >>>> normal task: (1024 / (1024 + 1024 + 3))^(-1) * 4ms = 8ms >>>> >>>> (4ms - 250 Hz) >>> My tick is 1ms - 1000HZ, which seems reasonable for 600ms? :) >> >> OK, I see. >> >> But here the different sched slices (check_preempt_tick()-> >> sched_slice()) between normal tasks and the idle task play a role to. >> >> Normal tasks get ~3ms whereas the idle task gets <0.01ms. > > In fact that depends on the number of CPUs on the system > :sysctl_sched_latency = 6ms * (1 + ilog(ncpus)) . On a 8 cores system, > normal task will run around 12ms in one shoot and the idle task still > one tick period True. This is on a single CPU. > Also, you can increase even more the period between 2 runs of idle > task by using cgroups and min shares value : 2 Ah yes, maybe this is what Jiang wants to do then? If his runtime does not have other requirements preventing this. [...]