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Shenoy" , K Prateek Nayak Subject: [PATCH v3 3/8] sched/topology: Switch to assigning "sd->shared" from s_data Date: Tue, 20 Jan 2026 11:32:41 +0000 Message-ID: <20260120113246.27987-4-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: BL02EPF00021F6A:EE_|BN7PPF521FFE181:EE_ X-MS-Office365-Filtering-Correlation-Id: 37d6ccf9-867e-49da-505b-08de5817cfa0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|376014|82310400026|36860700013|1800799024|13003099007; X-Microsoft-Antispam-Message-Info: =?us-ascii?Q?QlAiXmtCbAaeAG9rLJ0MqkZVB8ZDWaIZlouRWIYGH7o+SnUTFen5HY33j4BF?= =?us-ascii?Q?XpS0KrrNZycIKj0fH6OTQNwgnO5C9k+fYBuDK9xFU5MIKVIAzXxA/oE9EObN?= =?us-ascii?Q?4y3BH1hnVYVNB+rx7OPtWFEEfdJYiZJhgYfLq7969C2sFj1dREE/KPMkbJrS?= =?us-ascii?Q?u7SKf6d8YxYnWj+yerUJUx8ZOAo/jvUjBXk1yNQh3kpX/AxXTfBKmSNo0sRQ?= =?us-ascii?Q?1GJFdJMSVfeaq81B0bBW4ov1a1hxZtSk1oP0wPlOH1bhgRvOghJvq+OExJJo?= =?us-ascii?Q?pvo/5qFawkZNin83KwpovDAXOVhbyMxagJt/Y0vyar1xfl6+llQPXA9olatX?= =?us-ascii?Q?8MqqoMIV3JFsGs33M6UhFWBCf/Tl61OEp8TO3gjS18RrgKk66i1VkmoQJMwZ?= =?us-ascii?Q?N3sa1CVfewYjvoK7Fs5wvcOFe/KIdcqRb27wuKfV7QDdRxA3Yn9++qy321ik?= =?us-ascii?Q?A+N974NYJXuaJTys8v3JtC9ibIAvJmXIXlPZahoAv+G04CB6jF9IsZgHuR3v?= =?us-ascii?Q?vE9TVrZOed89h3j65S9WzxYrJvluKRZ21sUdRid6tdYaXCYNuZ3m0Nh14Mr1?= =?us-ascii?Q?f3wOXqmQelhD7v38bZcpydX5kMVcjS8CUvz3yjUftJ6IQ76ogc1dvPRwRnGP?= =?us-ascii?Q?yM+6uftIR1oeMd3lLP1cxPTXFLslq0GR7IbWiPFUbppqq1hbw+JvFoAQXyzY?= =?us-ascii?Q?C1sVCriOzlg2yV9M/a4LnegK4uzu7DUMqXabi9xxjkwDFbdVEXzMenprZsE9?= =?us-ascii?Q?1JL9BOLbCbpHTW0DRB7KRVOPPg4XyVyt5ryOj/wKNs+/SWBxag2KPr2rZhb5?= =?us-ascii?Q?+nMtdzXvt7TtYAtdSkdoq1HCL6p/Ei4ejMhrVpHD3H2/M105zA4JCT4ImegV?= =?us-ascii?Q?U23ftl17GPP19iQlb19M8UnB39K1iT4934T39EBaSDZV+cW6Y92amwLK2u7+?= =?us-ascii?Q?hChkpvsRC16TNg/cO/3vOHskwW2wiTZNjk1GB+sQF2BklkGp69tGRpqz+pPC?= =?us-ascii?Q?vGiLX9qdUn5J1Z6F1TK7c31/BoDBwK/gmruHP0DVhC+9mezmuajvTjhx2L7+?= =?us-ascii?Q?ywIsShH0bBPdrE0khqp8S48u3kwCPWVVOKOyTGB/a0EajuoltzsITynMus1n?= =?us-ascii?Q?wdKyOeyq0uPOYAg8c91RyCCfu/OMQoMtAVl0tFfDDaZWA0d8QSTLCykAw6oY?= =?us-ascii?Q?bXZ6uIhw3oDbXIo/syBM8PS5AXqnLxCxfhmX4PwzP/s2+v46CXTVJN4PmXaO?= =?us-ascii?Q?cOxOLE2a1VrkRLQPmrixV5nAo/6sDeeSyJbMPnefZ1QF9xteI7qc+/9WpC37?= =?us-ascii?Q?CJAgvgtvRfzeiHDEcG2zyLZfg/qvuA5KnHtYrkMDJfvWx3m5FRpyqADQ1vpv?= =?us-ascii?Q?rxu74MH9DIIzOmE9HNeQbUOI/7gGTIT9q5OSiRc/R+kMAzrJ0iO8+TqLQ88j?= =?us-ascii?Q?6oIefhhwajWL50elcbBlCszFqOBmQq44dkgupw+JJ7FDlDF1W2RhNDo6+P6w?= =?us-ascii?Q?oCy4k8w+wmgPBxc4UjlgcgNzr7LKP/kkWMSo4U3TWUrwFyNJsWyanVPn26kV?= =?us-ascii?Q?dyWRL02vkG+PbYFkgzgCIu3RLHMoQbZeTe+Fa8kPaJdAGfv8T9kaeBcueglO?= =?us-ascii?Q?jRw0AQ7COt4NNgQv9vWyiCWhtDmhd2tGxEtTIRyCmWRYpnryleJ4FdtKRgRh?= =?us-ascii?Q?xVzJvQ=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)(7416014)(376014)(82310400026)(36860700013)(1800799024)(13003099007);DIR:OUT;SFP:1101; X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 20 Jan 2026 11:34:02.3640 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 37d6ccf9-867e-49da-505b-08de5817cfa0 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: BL02EPF00021F6A.namprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN7PPF521FFE181 Content-Type: text/plain; charset="utf-8" Use the "sched_domain_shared" object allocated in s_data for "sd->shared" assignments. Assign "sd->shared" for the topmost SD_SHARE_LLC domain before degeneration and rely on the degeneration path to correctly pass down the shared object to "sd_llc". sd_degenerate_parent() ensures degenerating domains must have the same sched_domain_span() which ensures 1:1 passing down of the shared object. If the topmost SD_SHARE_LLC domain degenerates, the shared object is freed from destroy_sched_domain() when the last reference is dropped. build_sched_domains() NULLs out the objects that have been assigned as "sd->shared" and the unassigned ones are freed from the __sds_free() path. Post cpu_attach_domain(), all reclaims of "sd->shared" are handled via call_rcu() on the sched_domain object via destroy_sched_domains_rcu(). Signed-off-by: K Prateek Nayak --- Changelog rfc v2..v3: o Broke off from a single large patch. Previously https://lore.kernel.org/lkml/20251208092744.32737-3-kprateek.nayak@amd.co= m/ --- kernel/sched/topology.c | 34 ++++++++++++++++++++++++---------- 1 file changed, 24 insertions(+), 10 deletions(-) diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 623e8835d322..0f56462fef6f 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -679,6 +679,9 @@ static void update_top_cache_domain(int cpu) if (sd) { id =3D cpumask_first(sched_domain_span(sd)); size =3D cpumask_weight(sched_domain_span(sd)); + + /* If sd_llc exists, sd_llc_shared should exist too. */ + WARN_ON_ONCE(!sd->shared); sds =3D sd->shared; } =20 @@ -727,6 +730,13 @@ cpu_attach_domain(struct sched_domain *sd, struct root= _domain *rd, int cpu) if (sd_parent_degenerate(tmp, parent)) { tmp->parent =3D parent->parent; =20 + /* Pick reference to parent->shared. */ + if (parent->shared) { + WARN_ON_ONCE(tmp->shared); + tmp->shared =3D parent->shared; + parent->shared =3D NULL; + } + if (parent->parent) { parent->parent->child =3D tmp; parent->parent->groups->flags =3D tmp->flags; @@ -1732,16 +1742,6 @@ sd_init(struct sched_domain_topology_level *tl, sd->cache_nice_tries =3D 1; } =20 - /* - * For all levels sharing cache; connect a sched_domain_shared - * instance. - */ - if (sd->flags & SD_SHARE_LLC) { - sd->shared =3D *per_cpu_ptr(sdd->sds, sd_id); - atomic_inc(&sd->shared->ref); - atomic_set(&sd->shared->nr_busy_cpus, sd_weight); - } - sd->private =3D sdd; =20 return sd; @@ -2655,8 +2655,19 @@ build_sched_domains(const struct cpumask *cpu_map, s= truct sched_domain_attr *att unsigned int imb_span =3D 1; =20 for (sd =3D *per_cpu_ptr(d.sd, i); sd; sd =3D sd->parent) { + struct sched_domain *parent =3D sd->parent; struct sched_domain *child =3D sd->child; =20 + /* Attach sd->shared to the topmost SD_SHARE_LLC domain. */ + if ((sd->flags & SD_SHARE_LLC) && + (!parent || !(parent->flags & SD_SHARE_LLC))) { + int llc_id =3D cpumask_first(sched_domain_span(sd)); + + sd->shared =3D *per_cpu_ptr(d.sds, llc_id); + atomic_set(&sd->shared->nr_busy_cpus, sd->span_weight); + atomic_inc(&sd->shared->ref); + } + if (!(sd->flags & SD_SHARE_LLC) && child && (child->flags & SD_SHARE_LLC)) { struct sched_domain __rcu *top_p; @@ -2709,6 +2720,9 @@ build_sched_domains(const struct cpumask *cpu_map, st= ruct sched_domain_attr *att if (!cpumask_test_cpu(i, cpu_map)) continue; =20 + if (atomic_read(&(*per_cpu_ptr(d.sds, i))->ref)) + *per_cpu_ptr(d.sds, i) =3D NULL; + for (sd =3D *per_cpu_ptr(d.sd, i); sd; sd =3D sd->parent) { claim_allocations(i, sd); init_sched_groups_capacity(i, sd); --=20 2.34.1