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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by CH2PEPF00000145.mail.protection.outlook.com (10.167.244.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8534.20 via Frontend Transport; Fri, 14 Mar 2025 10:26:32 +0000 Received: from [10.136.37.23] (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; Fri, 14 Mar 2025 05:26:28 -0500 Message-ID: <6688eade-8eec-4d76-87f2-637425b1c2d2@amd.com> Date: Fri, 14 Mar 2025 15:56:26 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 2/7] sched/fair: Handle throttle path for task based throttle To: Aaron Lu , Chengming Zhou CC: Valentin Schneider , Ben Segall , Peter Zijlstra , Josh Don , Ingo Molnar , Vincent Guittot , , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Mel Gorman , Chuyi Zhou References: <20250313072030.1032893-1-ziqianlu@bytedance.com> <58e0515a-ed67-4d1a-825f-bfc2b31d1d18@linux.dev> <20250314094249.GC1633113@bytedance> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20250314094249.GC1633113@bytedance> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Mar 2025 10:26:32.4769 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e05b69e2-f0bd-4518-8ba4-08dd62e2b0d5 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: CH2PEPF00000145.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SJ0PR12MB6902 Hello Aaron, On 3/14/2025 3:12 PM, Aaron Lu wrote: >> Then then if we pick a task from a throttled cfs_rq subtree, we can setup task work >> for it, so we don't botter with the delayed_dequeue task case that Prateek mentioned. > If we add a check point in pick time, maybe we can also avoid the check > in enqueue time. One thing I'm thinking is, for a task, it may be picked > multiple times with only a single enqueue so if we do the check in pick, > the overhead can be larger? I think it can be minimized to a good extent. Something like: diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index d646451d617c..ba6571368840 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -5942,6 +5942,9 @@ static inline bool task_has_throttle_work(struct task_struct *p) static inline void task_throttle_setup_work(struct task_struct *p) { + if (task_has_throttle_work(p)) + return; + /* * Kthreads and exiting tasks don't return to userspace, so adding the * work is pointless @@ -5949,9 +5952,6 @@ static inline void task_throttle_setup_work(struct task_struct *p) if ((p->flags & (PF_EXITING | PF_KTHREAD))) return; - if (task_has_throttle_work(p)) - return; - task_work_add(p, &p->sched_throttle_work, TWA_RESUME); } @@ -6000,12 +6000,6 @@ static int tg_throttle_down(struct task_group *tg, void *data) node = rb_next(node); } - /* curr is not in the timeline tree */ - if (cfs_rq->curr && entity_is_task(cfs_rq->curr)) { - p = task_of(cfs_rq->curr); - task_throttle_setup_work(p); - } - return 0; } @@ -6049,6 +6043,18 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq) SCHED_WARN_ON(cfs_rq->throttled_clock); if (cfs_rq->nr_queued) cfs_rq->throttled_clock = rq_clock(rq); + + /* + * If cfs_rq->curr is set, check if current task is queued + * and set up the throttle work proactively. + */ + if (cfs_rq->curr) { + struct task_struct *p = rq->donor; /* scheduling context with proxy */ + + if (task_on_rq_queued(p)) + task_throttle_setup_work(p); + } + return; } @@ -8938,6 +8944,13 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf struct sched_entity *pse = &prev->se; struct cfs_rq *cfs_rq; + /* + * Check if throttle work needs to be setup when + * switching to a different task. + */ + if (throttled_hierarchy(cfs_rq_of(se))) + task_throttle_setup_work(p); + while (!(cfs_rq = is_same_group(se, pse))) { int se_depth = se->depth; int pse_depth = pse->depth; @@ -13340,6 +13353,9 @@ static void set_next_task_fair(struct rq *rq, struct task_struct *p, bool first) account_cfs_rq_runtime(cfs_rq, 0); } + if (throttled_hierarchy(cfs_rq_of(se))) + task_throttle_setup_work(p); + __set_next_task_fair(rq, p, first); } -- .. with the additional plumbing in place of course. -- Thanks and Regards, Prateek