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,URIBL_BLOCKED,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 87991C433E1 for ; Wed, 19 Aug 2020 10:46:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6C1CD2076E for ; Wed, 19 Aug 2020 10:46:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727843AbgHSKqj (ORCPT ); Wed, 19 Aug 2020 06:46:39 -0400 Received: from foss.arm.com ([217.140.110.172]:60810 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726642AbgHSKqh (ORCPT ); Wed, 19 Aug 2020 06:46:37 -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 7A6A1101E; Wed, 19 Aug 2020 03:46:36 -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 5A8133F6CF; Wed, 19 Aug 2020 03:46:28 -0700 (PDT) Subject: Re: [PATCH] sched/fair: reduce preemption with IDLE tasks runable(Internet mail) To: =?UTF-8?B?YmVuYmppYW5nKOiSi+W9qik=?= Cc: Jiang Biao , "mingo@redhat.com" , "peterz@infradead.org" , "juri.lelli@redhat.com" , "vincent.guittot@linaro.org" , "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> From: Dietmar Eggemann Message-ID: <729675a2-b083-4211-62c0-f7ed7f483ae2@arm.com> Date: Wed, 19 Aug 2020 12:46:22 +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: <755BFAD0-9072-4D73-9CD7-AF4F74A79D21@tencent.com> 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 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. So the idle task runs every ~680ms but only for 1 tick (1ms) (4 times less than the normal tasks). The condition 'if (delta_exec > ideal_runtime)' in check_preempt_tick() is only true at the 4th tick when a normal task runs even though the slice is 3ms. In the 250 Hz example the sched slice diffs are hidden behind the 4ms tick. [...]