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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id EC09DC64EC7 for ; Wed, 1 Mar 2023 13:03:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229971AbjCANDh (ORCPT ); Wed, 1 Mar 2023 08:03:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36304 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229546AbjCAND3 (ORCPT ); Wed, 1 Mar 2023 08:03:29 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6D8303E0A6; Wed, 1 Mar 2023 05:03:19 -0800 (PST) Received: from dggpeml500018.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4PRZCL0pQGzdbCR; Wed, 1 Mar 2023 21:02:38 +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; Wed, 1 Mar 2023 21:03:17 +0800 Message-ID: <62880d15-1a8b-6d71-05af-a80bad51c3cb@huawei.com> Date: Wed, 1 Mar 2023 21:03:16 +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 AUTOSEL 6.2 13/21] sched/fair: sanitize vruntime of entity being placed To: Sasha Levin , , CC: Roman Kagan , Peter Zijlstra , , , References: <20230226034150.771411-1-sashal@kernel.org> <20230226034150.771411-13-sashal@kernel.org> From: Zhang Qiao In-Reply-To: <20230226034150.771411-13-sashal@kernel.org> 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 2023/2/26 11:41, Sasha Levin 写道: > From: Zhang Qiao > > [ Upstream commit 829c1651e9c4a6f78398d3e67651cef9bb6b42cc ] Hi, This patch has significant impact on the hackbench.throughput [1]. Please don't backport this patch. [1] https://lore.kernel.org/lkml/202302211553.9738f304-yujie.liu@intel.com/T/#u Thanks. Zhang Qiao. > > When a scheduling entity is placed onto cfs_rq, its vruntime is pulled > to the base level (around cfs_rq->min_vruntime), so that the entity > doesn't gain extra boost when placed backwards. > > However, if the entity being placed wasn't executed for a long time, its > vruntime may get too far behind (e.g. while cfs_rq was executing a > low-weight hog), which can inverse the vruntime comparison due to s64 > overflow. This results in the entity being placed with its original > vruntime way forwards, so that it will effectively never get to the cpu. > > To prevent that, ignore the vruntime of the entity being placed if it > didn't execute for much longer than the characteristic sheduler time > scale. > > [rkagan: formatted, adjusted commit log, comments, cutoff value] > Signed-off-by: Zhang Qiao > Co-developed-by: Roman Kagan > Signed-off-by: Roman Kagan > Signed-off-by: Peter Zijlstra (Intel) > Link: https://lkml.kernel.org/r/20230130122216.3555094-1-rkagan@amazon.de > Signed-off-by: Sasha Levin > --- > kernel/sched/fair.c | 15 +++++++++++++-- > 1 file changed, 13 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 0f87369914274..717c3ca970e15 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4656,6 +4656,7 @@ static void > place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > { > u64 vruntime = cfs_rq->min_vruntime; > + u64 sleep_time; > > /* > * The 'current' period is already promised to the current tasks, > @@ -4685,8 +4686,18 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial) > vruntime -= thresh; > } > > - /* ensure we never gain time by being placed backwards. */ > - se->vruntime = max_vruntime(se->vruntime, vruntime); > + /* > + * Pull vruntime of the entity being placed to the base level of > + * cfs_rq, to prevent boosting it if placed backwards. If the entity > + * slept for a long time, don't even try to compare its vruntime with > + * the base as it may be too far off and the comparison may get > + * 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) > + se->vruntime = vruntime; > + else > + se->vruntime = max_vruntime(se->vruntime, vruntime); > } > > static void check_enqueue_throttle(struct cfs_rq *cfs_rq); >