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Received-SPF: Pass (protection.outlook.com: domain of amd.com designates 165.204.84.17 as permitted sender) receiver=protection.outlook.com; client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by BN3PEPF0000B374.mail.protection.outlook.com (10.167.243.171) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.7828.11 via Frontend Transport; Thu, 1 Aug 2024 03:42:40 +0000 Received: from [10.136.40.92] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Wed, 31 Jul 2024 22:40:39 -0500 Message-ID: <810b0f1f-d490-83b9-efce-734ce7734c8d@amd.com> Date: Thu, 1 Aug 2024 09:10:12 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [peterz-queue:sched/prep] [sched/fair] 124c8f4374: WARNING:at_kernel/sched/sched.h:#update_load_avg Content-Language: en-US To: Peter Zijlstra CC: , , , , , kernel test robot References: <202407291328.761441a7-oliver.sang@intel.com> <5e3b9b29-8d17-6a04-f2a5-1748a52d1a6a@amd.com> <20240731115418.GD33588@noisy.programming.kicks-ass.net> From: K Prateek Nayak In-Reply-To: <20240731115418.GD33588@noisy.programming.kicks-ass.net> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 01 Aug 2024 03:42:40.8494 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 8c53ca55-9a03-4e84-40aa-08dcb1dbfeb9 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN3PEPF0000B374.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB5718 Hello Peter, On 7/31/2024 5:24 PM, Peter Zijlstra wrote: > On Wed, Jul 31, 2024 at 11:46:48AM +0530, K Prateek Nayak wrote: >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index cd4a6bf14828..c437b408d29b 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -13297,10 +13297,34 @@ void unregister_fair_sched_group(struct task_group *tg) >> if (se->sched_delayed) { >> guard(rq_lock_irqsave)(rq); >> if (se->sched_delayed) { >> + /* >> + * We can reach here when processing RCU_SOFTIRQ on exit path from >> + * a reschedule IPI. wakeup_preempt() may have set RQCF_REQ_SKIP to >> + * skip a close clock update in schedule(), however, in presence of >> + * a delayed entity, this trips the check in rq_clock_pelt() which >> + * now believes the clock value is stale and needs updating. To >> + * prevent such situation, cancel any pending skip updates, and >> + * update the rq clock. >> + */ >> + rq_clock_cancel_skipupdate(rq); >> + >> + /* >> + * XXX: Will this trip WARN_DOUBLE_CLOCK? In which case, can >> + * rq_clock_cancel_skipupdate() be made to return a bool if >> + * RQCF_REQ_SKIP is set and we avoid this update? >> + */ >> update_rq_clock(rq); >> + >> dequeue_entities(rq, se, DEQUEUE_SLEEP | DEQUEUE_DELAYED); >> + >> + /* Avoid updating the clock again if a schedule() is pending */ >> + if (task_on_rq_queued(rq->curr) && >> + test_tsk_need_resched(rq->curr)) >> + rq_clock_skip_update(rq); >> } >> list_del_leaf_cfs_rq(cfs_rq); >> + >> + >> } >> remove_entity_load_avg(se); >> } > > So I did update this to simply add update_rq_clock() before the > dequeue_entity(SLEEP|DELAYED). I initially had, these, then confused > myself between deactivate_task() and dequeue_entity(), where the former > updates the clock but the latter does not, and removed them. Then Mike > complained, and I restored it for the regular exit path and forgot the > cgroup exit path. > > But now they should both be doing update_rq_clock() here. > > https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/commit/?h=sched/eevdf&id=5b3a132d4dd5c91f26beb3e8973c03cdb77d7873 > > Since this is all with our own rq->lock held, I don't think skip would > be relevant here. Thank you for clarifying the nuances. I'll continue testing with the latest branch. -- Thanks and Regards, Prateek