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 3E90FC6FA8E for ; Thu, 2 Mar 2023 09:36:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229836AbjCBJgY (ORCPT ); Thu, 2 Mar 2023 04:36:24 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38996 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229457AbjCBJgU (ORCPT ); Thu, 2 Mar 2023 04:36:20 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1D76D38660 for ; Thu, 2 Mar 2023 01:36:16 -0800 (PST) Received: from dggpeml500018.china.huawei.com (unknown [172.30.72.57]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4PS5Wf09jhz16NxT; Thu, 2 Mar 2023 17:33:34 +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 17:36:13 +0800 Message-ID: <1cd19d3f-18c4-92f9-257a-378cc18cfbc7@huawei.com> Date: Thu, 2 Mar 2023 17:36:13 +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 References: <20230209193107.1432770-1-rkagan@amazon.de> 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 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: dggems701-chm.china.huawei.com (10.3.19.178) 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 2023/2/27 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) + 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 >> >> >> > . >