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client-ip=165.204.84.17; helo=satlexmb08.amd.com; pr=C Received: from satlexmb08.amd.com (165.204.84.17) by SJ1PEPF000023D8.mail.protection.outlook.com (10.167.244.73) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9298.0 via Frontend Transport; Thu, 30 Oct 2025 05:46:42 +0000 Received: from satlexmb08.amd.com (10.181.42.217) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.17; Wed, 29 Oct 2025 22:46:42 -0700 Received: from [10.136.32.170] (10.180.168.240) by satlexmb08.amd.com (10.181.42.217) with Microsoft SMTP Server id 15.2.2562.17 via Frontend Transport; Wed, 29 Oct 2025 22:46:37 -0700 Message-ID: <0d1f5a59-82b5-494f-b3d3-6332027d0350@amd.com> Date: Thu, 30 Oct 2025 11:16:36 +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: [PATCH v3] sched/fair: Prevent cfs_rq from being unthrottled with zero runtime_remaining To: Aaron Lu , Ben Segall , Peter Zijlstra , Hao Jia , Valentin Schneider , Chengming Zhou , Josh Don , Ingo Molnar , Vincent Guittot , Xi Wang CC: , Juri Lelli , Dietmar Eggemann , Steven Rostedt , Mel Gorman , Chuyi Zhou , Jan Kiszka , Florian Bezdeka , Songtang Liu , Chen Yu , Matteo Martelli , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Sebastian Andrzej Siewior References: <20251030032755.560-1-ziqianlu@bytedance.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20251030032755.560-1-ziqianlu@bytedance.com> Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Oct 2025 05:46:42.9246 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b032070a-81ce-4c48-8805-08de1777b488 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=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000023D8.namprd21.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR12MB6142 Hello Aaron, On 10/30/2025 8:57 AM, Aaron Lu wrote: > I think it's a chaos to trigger throttle on unthrottle path, the status > of a being unthrottled cfs_rq can be in a mixed state in the end, so fix > this by granting 1ns to cfs_rq in tg_set_cfs_bandwidth(). This ensures > cfs_rq_c has a positive runtime_remaining when initialized as unthrottled > and cannot enter tg_unthrottle_up() with zero runtime_remaining. > > Also, update outdated comments in tg_throttle_down() since > unthrottle_cfs_rq() is no longer called with zero runtime_remaining. > While at it, remove a redundant assignment to se in tg_throttle_down(). > > Fixes: e1fad12dcb66 ("sched/fair: Switch to task based throttle model") > Suggested-by: Benjamin Segall > Signed-off-by: Aaron Lu Have been stress testing this on my system and I haven't seen any splats yet. Feel free to include: Reviewed-by: K Prateek Nayak Tested-by: K Prateek Nayak -- Thanks and Regards, Prateek