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Tue, 27 Oct 2026 01:12:23 -0500 Message-ID: Date: Tue, 27 Oct 2026 11:42:22 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 5/6] sched_ext: Add a kfunc to read a task's preferred NUMA node To: Andrea Righi , Tejun Heo , David Vernet , Changwoo Min CC: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , "Mel Gorman" , Valentin Schneider , "Vladimir Vdovin" , Gregory Price , David Dai , Emil Tsalapatis , Christian Loehle , Balbir Singh , Lee Trager , , References: <20261027041536.3317971-1-arighi@nvidia.com> <20261027041536.3317971-6-arighi@nvidia.com> Content-Language: en-US From: K Prateek Nayak In-Reply-To: <20261027041536.3317971-6-arighi@nvidia.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SJ1PEPF0000231D:EE_|DM6PR12MB4417:EE_ X-MS-Office365-Filtering-Correlation-Id: 1237160e-fe77-4f19-d06b-08df33f1487a X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|82310400026|36860700016|23010399003|1800799024|261026121527099003|4143699003|5023799004|11063799006|56012099006|261021121427099003|261022075727099003|10067099003|22082099003|18002099003; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: Da7DhH7onSfjvLvidxNzCYNtrEJpTyFjC4TZeJ8Xm+mdmMGP/tyubhHkm9raShc6aLBO03sxrStQP1p+jNitX6VFFWuJBRrieJFUz1EalXdp4ERl7zLAalA2XCFpqfVOPQNJnXJQSVG4IiLexYMXuFHL0VGxC/S7qJg6V5DS9TIO4rxPKy7gdxQ2LcNzNgOCVrAGdY8sGW9ItnRouT0VjRn4E1EBzpLIk8zmGHwWi6t4yGyD9PhOPOoLnddiNkQpg3Rn4MMp87v7KdpMFKHu59xxWeRUcgOjZcAPXiHryu2tjE0JKiEtDP9IPX1svOe/YLQE50BsSgd7F6/bv7DlS9BdNZdHEuOeoXjj/lMxJ6/KgzsUGTMHcQj+zLjUrJM9jakkhr9Rip3X70WV6TgqwBWlz08E8oynPqszd/vfI4AMCSK9KCi0dICU9ZS4rWaO X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 27 Oct 2026 06:12:30.4788 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 1237160e-fe77-4f19-d06b-08df33f1487a 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: SJ1PEPF0000231D.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM6PR12MB4417 Hello Andrea, On 10/27/2026 9:43 AM, Andrea Righi wrote: > +__bpf_kfunc s32 scx_bpf_task_numa_nid(const struct task_struct *p) > +{ > +#ifdef CONFIG_NUMA_BALANCING > + if (task_on_scx(p)) { > + struct scx_sched *sch; > + > + guard(rcu)(); > + sch = scx_task_sched_rcu(p); > + if (!sch || !SCX_HAS_OP(sch, set_numa_node)) > + return NUMA_NO_NODE; > + } > + > + return READ_ONCE(p->numa_preferred_nid); Would the ext scheduler need the raw numa_preferred_nid when sched_numa_balancing is disabled? It may just be pointing to some stale value if NUMA balancing was disabled at runtime right? > +#else > + return NUMA_NO_NODE; > +#endif > +} > + > /** > * scx_bpf_locked_rq - Return the rq currently locked by SCX > * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs > @@ -11836,6 +11877,7 @@ BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE) > BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU) On a tangential note, scx_bpf_task_running() just does a rcu_access_pointer() (resolves to a READ_ONCE()) and doesn't take a rcu_read_lock() so does it really need KF_RCU? > BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU) > BTF_ID_FLAGS(func, scx_bpf_task_cid, KF_RCU) > +BTF_ID_FLAGS(func, scx_bpf_task_numa_nid, KF_RCU) > BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_IMPLICIT_ARGS | KF_RET_NULL) > BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED) > BTF_ID_FLAGS(func, scx_bpf_cid_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED) -- Thanks and Regards, Prateek