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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 BN2PEPF000044A2.mail.protection.outlook.com (10.167.243.153) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.245.5 via Frontend Transport; Sat, 18 Jul 2026 06:22:19 +0000 Received: from satlexmb07.amd.com (10.181.42.216) 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 15.2.2562.41; Sat, 18 Jul 2026 01:22:19 -0500 Received: from [172.31.184.125] (10.180.168.240) by satlexmb07.amd.com (10.181.42.216) with Microsoft SMTP Server id 15.2.2562.41 via Frontend Transport; Sat, 18 Jul 2026 01:22:12 -0500 Message-ID: <37ebb2cf-6471-49ff-bafc-f588e556d90a@amd.com> Date: Sat, 18 Jul 2026 11:52:05 +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 3/3] sched/core: Swap to lock owner for core-wide pick on core-cookie mismatch To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , John Stultz , CC: Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Ben Segall , Joel Fernandes , Qais Yousef , Zimuzo Ezeozue , Will Deacon , Waiman Long , Boqun Feng , "Paul E. McKenney" , Metin Kaya , Xuewen Yan , Thomas Gleixner , Daniel Lezcano , Suleiman Souhlal , kuyo chang , hupu , Vasily Gorbik , References: <20260717111601.6017-1-kprateek.nayak@amd.com> <20260717111601.6017-4-kprateek.nayak@amd.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20260717111601.6017-4-kprateek.nayak@amd.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BN2PEPF000044A2:EE_|CY8PR12MB8066:EE_ X-MS-Office365-Filtering-Correlation-Id: d838ea0a-f198-4fb3-e095-08dee494ebf3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|36860700016|23010399003|7416014|376014|82310400026|1800799024|13003099007|56012099006|11063799006|4143699003|10067099003|18002099003|22082099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb08.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(36860700016)(23010399003)(7416014)(376014)(82310400026)(1800799024)(13003099007)(56012099006)(11063799006)(4143699003)(10067099003)(18002099003)(22082099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: L+uVkiXxq0rblRudxRZLog8SVoqDFFyA2N2XuIzGjLAHNX+KxkevfzcUnSxdK63T1xqLCjClj0GGd3dqK+fx/WtzYcthXQSj2Q3uoWMDnPxlF2p33Qyw4fd7pKFqWEyMuQNKurWCEGcrPjeGCLlzGm9J1EMZW4rLQIc5UacP1Dw1UQpK39Dl3PCMxCRinCDpoHq3Svx0HTMkrqhtmIHtdYd4WzAVXXZxrP5KFUt9clpp8BIebK0IWTimaZjCjHqhyMznhjL0Vlhd8IY9LlUGMEgdL3xk8bOpX228z1IbDgdlbiBSB+VqLbsxvzYEKM6DPPQD7lt6b9PA0llOHTi/N0eiwDTdVzBQt8Xj8kSZvCDeN0bSNuiQvWaXXAAtcWIux7nGhhaGY8wnMPq8fhgXUjYobTqdo5Dy8pYi9aMt2nvDImIHZkLGFfRSnHRLeP4Y X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Jul 2026 06:22:19.7719 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d838ea0a-f198-4fb3-e095-08dee494ebf3 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: BN2PEPF000044A2.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB8066 Hello folks, On 7/17/2026 4:46 PM, K Prateek Nayak wrote: > @@ -6728,6 +6735,24 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) > */ > rq->core->core_task_seq++; > > + /* Last core_pick resolved to a blocked_donor! */ > + if (sched_core_proxy_pick(rq)) { > + WARN_ON_ONCE(!donor->is_blocked); > + > + donor->blocked_donor = NULL; > + owner = find_proxy_task(rq, donor, rf); > + if (owner && owner != rq->idle) > + goto restart_multi; > + /* > + * Something changed in the proxy chain! > + * Retry pick like normal. Increment core_task_seq > + * since the core-wide lock might have been dropped > + * during proxy-migration in find_proxy_task(). > + */ > + rq->core_pick_blocked_donor = false; > + rq->core->core_task_seq++; > + } > + > /* > * Optimize for common case where this CPU has no cookies > * and there are no cookied tasks running on siblings. > @@ -6786,6 +6811,21 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) > } > > rq_max->core_pick_leader = true; > + > + if (sched_core_proxy_pick(rq)) { > + WARN_ON_ONCE(!owner); > + > + /* > + * Core-wide pick resolved to the same state as last time. > + * Swap the donor with the lock owner and continue the > + * rest of the pick sequence. > + */ > + if (rq->core_pick_leader && rq->core_pick == donor) { > + rq_max->core_pick = owner; > + max = owner; > + } > + } And I missed: diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ab3b3104cd868..f12064c8222e6 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6823,6 +6823,13 @@ pick_next_task(struct rq *rq, struct rq_flags *rf) if (rq->core_pick_leader && rq->core_pick == donor) { rq_max->core_pick = owner; max = owner; + } else { + /* + * Pick resolved to a different leader / donor task. + * Clear the "core_pick_blocked_donor" indicator and + * proceed like normal. + */ + rq->core_pick_blocked_donor = false; } } --- I seemed to have managed without it because, once the proxy chain has stabilized, we never drop the core-wide lock, and pick always resolves to the same state for most part but a ->balance() on the re-pick can bring tasks in and that can alter how the pick resolves. priority-inversion-demo with the fix: https://imgur.com/ioppJWC > + > cookie = rq->core->core_cookie = max->core_cookie; > > /* -- Thanks and Regards, Prateek