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 9A5C7C678D4 for ; Fri, 3 Mar 2023 06:51:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229565AbjCCGvz (ORCPT ); Fri, 3 Mar 2023 01:51:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229452AbjCCGvx (ORCPT ); Fri, 3 Mar 2023 01:51:53 -0500 Received: from szxga08-in.huawei.com (szxga08-in.huawei.com [45.249.212.255]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E795015579 for ; Thu, 2 Mar 2023 22:51:46 -0800 (PST) Received: from dggpeml500018.china.huawei.com (unknown [172.30.72.55]) by szxga08-in.huawei.com (SkyGuard) with ESMTP id 4PSdqM2zD3z16NrX; Fri, 3 Mar 2023 14:49:03 +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; Fri, 3 Mar 2023 14:51:44 +0800 Message-ID: <5b8bb880-de5a-dd99-4168-89d1281e8348@huawei.com> Date: Fri, 3 Mar 2023 14:51:44 +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: dggems704-chm.china.huawei.com (10.3.19.181) 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 22:55, Vincent Guittot 写道: > On Thu, 2 Mar 2023 at 15:29, Zhang Qiao wrote: >> >> >> >> 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? > > se->exec_start is update when the task becomes current. > > You can have the sequence: > > task TA runs on CPU0 > TA's se->exec_start = xxxx > TA is put back into the rb tree waiting for next slice while another > task is running > CPU1 pulls TA which migrates on CPU1 > migrate_task_rq_fair() w/ TA's se->exec_start == xxxx > TA's se->exec_start = 0 > TA is put into the rb tree of CPU1 waiting to run on CPU1 > CPU2 pulls TA which migrates on CPU2 > migrate_task_rq_fair() w/ TA's se->exec_start == 0 > TA's se->exec_start = 0 Hi, Vincent, yes, you're right, such sequence does exist. But at this point, p->__state != TASK_WAKING. I have a question, Whether there is case that is "p->se.exec_start == 0 && p->__state == TASK_WAKING" ? I analyzed the code and concluded that this case isn't existed, is it right? Thanks. ZhangQiao. > >> >> 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? > > the vruntime have been updated when enqueued but not exec_start > >> >>> 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 >>>>>> >>>>>> >>>>>> >>>>> . >>>>> >>> . >>> > . >