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Shenoy" , K Prateek Nayak Subject: [PATCH v3 8/8] sched/fair: Simplify SIS_UTIL handling in select_idle_cpu() Date: Tue, 20 Jan 2026 11:32:46 +0000 Message-ID: <20260120113246.27987-9-kprateek.nayak@amd.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260120113246.27987-1-kprateek.nayak@amd.com> References: <20260120113246.27987-1-kprateek.nayak@amd.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: satlexmb08.amd.com (10.181.42.217) To satlexmb07.amd.com (10.181.42.216) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL02EPF00021F68:EE_|PH7PR12MB7938:EE_ X-MS-Office365-Filtering-Correlation-Id: 19dcafeb-3da2-4f7f-7f1f-08de58180775 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|7416014|1800799024|36860700013|82310400026; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?EM1MDKXDnSgB0qae7CiYWfHsFZdkiQ3xfRcNEATfJ3V8ZERZNvX3JX/pEenN?= =?us-ascii?Q?5R/6nwMwDvZnZQYGmGAX64G4UBizpm0tZ1vVfrf2hIQeYRc/kDnsYLJLbtfI?= =?us-ascii?Q?of+blg5JwTYrdUQe/oeHjq6WYVwQDjSrpLIiyFUtVBWVbodEH2RwYZSyELkU?= =?us-ascii?Q?vcm3d+hb5la+4pSUbkdM0zSqTDB6MsDJyv3Zidl3lPGCOe3i7CHQbI+M1o/v?= =?us-ascii?Q?ShTVce5UmLpwiyO2ejuQnFU3+VyY8Tn8rD9x7slHG4ff5gCSg0A+wTonfR9i?= =?us-ascii?Q?NWiZmgqlIdiSiGvu6LNS7KBcELNKWQ5rkn1AOJLbTy5xpUK4AiaFDSBxlS3W?= =?us-ascii?Q?sFQz7cGwze/l4tWetf+QkpyX6LAbcfwNrUKDUOjo68rR4S7W9QDl0gTEJRg7?= =?us-ascii?Q?EMA9Kdo8LZUD03P6o73EoplxEB22rVr5W9nzGJDuN1wgM5UgiEXD9MPugwHK?= =?us-ascii?Q?vsyCjEmvvEzkz0q2mjCo5grtpqsM+hMD6YY3S4/2QCgBJ9zGKLvDYfKfapxm?= =?us-ascii?Q?Uce1AnrqxweTYgGsPV8AcnwQmXXWexXFV4rq2kUlNnOgUzPE5X/2nBjCghNE?= =?us-ascii?Q?WfcwOm0S0tswDK85H2m62Q7xVtDHk9PaUO7BupJRKpsGbs/ivB9OmX5Su5jm?= =?us-ascii?Q?yAXYWTDQjxmAD+Q0Fwg/iXZnQJqAQaLWHRWqz/HnggfSmvh2f9C1thdqQHip?= =?us-ascii?Q?vZ35UqE3CoA29kbNVrr4qdsRYOdwy6+319ed8LGANk6n+8avd4n21BJwX3ng?= =?us-ascii?Q?iWTFa7i2DkohvWXVx4l5mNK5AC0qkdEKMS/Mf2Az5erpG95wKzck5EnOxbWZ?= =?us-ascii?Q?IyYNirrjduaxCoNejIwP0eHRcH+ArVqez35OZEqd4MIiJB4iyGbf0dhgwhAF?= =?us-ascii?Q?cZI7IOkR4wQUi/gqLecLz5nAgxD7HPOpAIO4IdpkfA9exesgQ8ZIid76xRpX?= =?us-ascii?Q?JNmh0unM0/dT5nw6Ep6MFiZEgTjBEXuVyq+ALpB80/iUkomkY7+sYzBtSalP?= =?us-ascii?Q?DmOyma0/nlSTso5ehBB1x9a49TFwPj6HI008lDRYMCJeYlNUj9BojRtP8fOb?= =?us-ascii?Q?fCBFnoOw/oeQeAIDrLq30KuriMDNudi8APaPb+Dhp7TLJYVRI2TUyPRzIcVg?= =?us-ascii?Q?AjwshBwlGSfx+GFNIG9XfHZbS4AphQFbHWvW6RigxGb38VrD608r5wMRzD0B?= =?us-ascii?Q?9sxYwq+CB3+1te8EdOXDSpGgxp8078CMKXkN98khHMavH+B8l6vKu1X4JNUq?= =?us-ascii?Q?Im4EHtR5rRN2GH4yfFuxC6sDlkPRnuHfHrmAVXPvdQvcr/zOOk2/oktp/iHQ?= =?us-ascii?Q?lcyt745tZPCZuLwkCiIbBVXdEksWVW+drUVYu9J2cPYTkPnZTddARm19QYaP?= =?us-ascii?Q?o1rsswCvk/1PQVLPe3Sba5FMkWX1e02z/p6OSmDfKtKKB7xRli2YY3d1Lig5?= =?us-ascii?Q?K80p8KgsTRJYdSrqmMR4YCe1peOqDT35ebV29Xp3Tk9tPSbk31BdUwroKVew?= =?us-ascii?Q?XPDFDh+xkFFXYSWwkG9q2+hah6p85VcN8hlNIWeKjheoXlNoaRpAnWkLSXO/?= =?us-ascii?Q?wHqwyb+XJAXLahNCFu+inYXVlfqQBLqfyGbBn6L3ihFXjMmsLy0u2p0ie3sc?= =?us-ascii?Q?/vlAV6nJ/MSaSeCC/9lH5Qt7TL1ZZY7+bIDgbCf8q2u6f0SwnNtcc/CBc3Ml?= =?us-ascii?Q?hkc70Q=3D=3D?= X-Forefront-Antispam-Report: CIP:165.204.84.17;CTRY:US;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:satlexmb07.amd.com;PTR:InfoDomainNonexistent;CAT:NONE;SFS:(13230040)(376014)(7416014)(1800799024)(36860700013)(82310400026);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Jan 2026 11:35:36.0358 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 19dcafeb-3da2-4f7f-7f1f-08de58180775 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BL02EPF00021F68.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7938 Content-Type: text/plain; charset="utf-8" Use the "sd_llc" passed to select_idle_cpu() to obtain the "sd_llc_shared" instead of dereferencing the per-CPU variable. Since "sd->shared" is always reclaimed at the same time as "sd" via call_rcu() and update_top_cache_domain() always ensures a valid "sd->shared" assignment when "sd_llc" is present, "sd_llc->shared" can always be dereferenced without needing an additional check. While at it move the cpumask_and() operation after the SIS_UTIL bailout check to avoid unnecessarily computing the cpumask. Signed-off-by: K Prateek Nayak Reviewed-by: Shrikanth Hegde --- Changelog rfc v2..v3: o No changes. to the diff. Added more details on directly dereferencing "sd->shared" without a NULL check in the commit message. --- kernel/sched/fair.c | 19 ++++++++----------- 1 file changed, 8 insertions(+), 11 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index c308c0700a7f..b4ae9444d32f 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7629,21 +7629,18 @@ static int select_idle_cpu(struct task_struct *p, s= truct sched_domain *sd, bool { struct cpumask *cpus =3D this_cpu_cpumask_var_ptr(select_rq_mask); int i, cpu, idle_cpu =3D -1, nr =3D INT_MAX; - struct sched_domain_shared *sd_share; - - cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); =20 if (sched_feat(SIS_UTIL)) { - sd_share =3D rcu_dereference_all(per_cpu(sd_llc_shared, target)); - if (sd_share) { - /* because !--nr is the condition to stop scan */ - nr =3D READ_ONCE(sd_share->nr_idle_scan) + 1; - /* overloaded LLC is unlikely to have idle cpu/core */ - if (nr =3D=3D 1) - return -1; - } + /* because !--nr is the condition to stop scan */ + nr =3D READ_ONCE(sd->shared->nr_idle_scan) + 1; + /* overloaded LLC is unlikely to have idle cpu/core */ + if (nr =3D=3D 1) + return -1; } =20 + if (!cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr)) + return -1; + if (static_branch_unlikely(&sched_cluster_active)) { struct sched_group *sg =3D sd->groups; =20 --=20 2.34.1