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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C314EC678D4 for ; Thu, 2 Mar 2023 14:29:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229849AbjCBO3j (ORCPT ); Thu, 2 Mar 2023 09:29:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49560 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229744AbjCBO3g (ORCPT ); Thu, 2 Mar 2023 09:29:36 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 595151E2B8 for ; Thu, 2 Mar 2023 06:29:32 -0800 (PST) Received: from dggpeml500018.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4PSD203bqVznWdY; Thu, 2 Mar 2023 22:26:48 +0800 (CST) Received: from [10.67.111.186] (10.67.111.186) by dggpeml500018.china.huawei.com (7.185.36.186) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.21; Thu, 2 Mar 2023 22:29:29 +0800 Message-ID: Date: Thu, 2 Mar 2023 22:29:29 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.1.1 Subject: Re: [PATCH v3] sched/fair: sanitize vruntime of entity being placed To: Vincent Guittot CC: Roman Kagan , Peter Zijlstra , , Valentin Schneider , Ben Segall , Waiman Long , Steven Rostedt , Mel Gorman , Dietmar Eggemann , Daniel Bristot de Oliveira , Ingo Molnar , Juri Lelli References: <20230209193107.1432770-1-rkagan@amazon.de> <1cd19d3f-18c4-92f9-257a-378cc18cfbc7@huawei.com> From: Zhang Qiao In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.67.111.186] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggpeml500018.china.huawei.com (7.185.36.186) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2023/3/2 21:34, Vincent Guittot 写道: > On Thu, 2 Mar 2023 at 10:36, Zhang Qiao wrote: >> >> >> >> 在 2023/2/27 22:37, Vincent Guittot 写道: >>> On Mon, 27 Feb 2023 at 09:43, Roman Kagan wrote: >>>> >>>> On Tue, Feb 21, 2023 at 06:26:11PM +0100, Vincent Guittot wrote: >>>>> On Tue, 21 Feb 2023 at 17:57, Roman Kagan wrote: >>>>>> What scares me, though, is that I've got a message from the test robot >>>>>> that this commit drammatically affected hackbench results, see the quote >>>>>> below. I expected the commit not to affect any benchmarks. >>>>>> >>>>>> Any idea what could have caused this change? >>>>> >>>>> Hmm, It's most probably because se->exec_start is reset after a >>>>> migration and the condition becomes true for newly migrated task >>>>> whereas its vruntime should be after min_vruntime. >>>>> >>>>> We have missed this condition >>>> >>>> Makes sense to me. >>>> >>>> But what would then be the reliable way to detect a sched_entity which >>>> has slept for long and risks overflowing in .vruntime comparison? >>> >>> For now I don't have a better idea than adding the same check in >>> migrate_task_rq_fair() >> >> Hi, Vincent， >> I fixed this condition as you said, and the test results are as follows. >> >> testcase: hackbench -g 44 -f 20 --process --pipe -l 60000 -s 100 >> version1: v6.2 >> version2: v6.2 + commit 829c1651e9c4 >> version3: v6.2 + commit 829c1651e9c4 + this patch >> >> ------------------------------------------------- >> version1 version2 version3 >> test1 81.0 118.1 82.1 >> test2 82.1 116.9 80.3 >> test3 83.2 103.9 83.3 >> avg(s) 82.1 113.0 81.9 >> >> ------------------------------------------------- >> After deal with the task migration case, the hackbench result has restored. >> >> The patch as follow, how does this look? >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index ff4dbbae3b10..3a88d20fd29e 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -4648,6 +4648,26 @@ static void check_spread(struct cfs_rq *cfs_rq, struct sched_entity *se) >> #endif >> } >> >> +static inline u64 sched_sleeper_credit(struct sched_entity *se) >> +{ >> + >> + unsigned long thresh; >> + >> + if (se_is_idle(se)) >> + thresh = sysctl_sched_min_granularity; >> + else >> + thresh = sysctl_sched_latency; >> + >> + /* >> + * Halve their sleep time's effect, to allow >> + * for a gentler effect of sleepers: >> + */ >> + if (sched_feat(GENTLE_FAIR_SLEEPERS)) >> + thresh >>= 1; >> + >> + return thresh; >> +} >> + >> static void >> place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) >> { >> @@ -4664,23 +4684,8 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) >> vruntime += sched_vslice(cfs_rq, se); >> >> /* sleeps up to a single latency don't count. */ >> - if (!initial) { >> - unsigned long thresh; >> - >> - if (se_is_idle(se)) >> - thresh = sysctl_sched_min_granularity; >> - else >> - thresh = sysctl_sched_latency; >> - >> - /* >> - * Halve their sleep time's effect, to allow >> - * for a gentler effect of sleepers: >> - */ >> - if (sched_feat(GENTLE_FAIR_SLEEPERS)) >> - thresh >>= 1; >> - >> - vruntime -= thresh; >> - } >> + if (!initial) >> + vruntime -= sched_sleeper_credit(se); >> >> /* >> * Pull vruntime of the entity being placed to the base level of >> @@ -4690,7 +4695,7 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) >> * inversed due to s64 overflow. >> */ >> sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; >> - if ((s64)sleep_time > 60LL * NSEC_PER_SEC) >> + if (se->exec_start != 0 && (s64)sleep_time > 60LL * NSEC_PER_SEC) >> se->vruntime = vruntime; >> else >> se->vruntime = max_vruntime(se->vruntime, vruntime); >> @@ -7634,8 +7639,12 @@ static void migrate_task_rq_fair(struct task_struct *p, int new_cpu) >> */ >> if (READ_ONCE(p->__state) == TASK_WAKING) { >> struct cfs_rq *cfs_rq = cfs_rq_of(se); >> + u64 sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; >> >> - se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); >> + if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > > You also need to test (se->exec_start !=0) here because the task might Hi, I don't understand when the another migration happend. Could you tell me in more detail? I think the next migration will happend after the wakee task enqueued, but at this time the p->__state isn't TASK_WAKING, p->__state already be changed to TASK_RUNNING at ttwu_do_wakeup(). If such a migration exists, Previous code "se->vruntime -= u64_u32_load(cfs_rq->min_vruntime);" maybe perform multiple times，wouldn't it go wrong in this way? > migrate another time before being scheduled. You should create a > helper function like below and use it in both place Ok, I will update at next version. Thanks, ZhangQiao. > > static inline bool entity_long_sleep(se) > { > struct cfs_rq *cfs_rq; > u64 sleep_time; > > if (se->exec_start == 0) > return false; > > cfs_rq = cfs_rq_of(se); > sleep_time = rq_clock_task(rq_of(cfs_rq)) - se->exec_start; > if ((s64)sleep_time > 60LL * NSEC_PER_SEC) > return true; > > return false; > } > > >> + se->vruntime = -sched_sleeper_credit(se); >> + else >> + se->vruntime -= u64_u32_load(cfs_rq->min_vruntime); >> } >> >> if (!task_on_rq_migrating(p)) { >> >> >> >> Thanks. >> Zhang Qiao. >> >>> >>>> >>>> Thanks, >>>> Roman. >>>> >>>> >>>> >>>> Amazon Development Center Germany GmbH >>>> Krausenstr. 38 >>>> 10117 Berlin >>>> Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss >>>> Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B >>>> Sitz: Berlin >>>> Ust-ID: DE 289 237 879 >>>> >>>> >>>> >>> . >>> > . >