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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?+nlnf9dRM0hqBB4sAdHXbEXVwcP0L1Gbwhn6hMsllAch9KyJ2xORqaqKoUkg?= =?us-ascii?Q?5tKsYLklVLnSpKozRIhaPNJ7GBHuYeDwJk8f9yAzvFMaVzvujYrZgVAfqDNL?= =?us-ascii?Q?bJE1BmIZaCPlmD+FcR6Gc88oAV8PHan05KNdFppY2v3kUwDUGA+OOqsT8yaF?= =?us-ascii?Q?r4tsEnfFdS2VTujQM0rnesVZ1DJ03+CxOOLDO8n9quNWKdk2s9el7ChqOXKz?= =?us-ascii?Q?1cNjBhtbq4EKkmravt7hdtayv0NyhmgYUSiApqxLlGZj7ODbIqAnZjI+hfYd?= =?us-ascii?Q?i0g7NJQO/sCDHSOqkYFm9rWDcVwh53HDWEX1NMI61pqEFCR9aL5C2U8HST/j?= =?us-ascii?Q?+j1TbClxAXqkTRL7TTynJerBBFM49EEP2q4YU/PMZ/Sfdlh102kq+YEOyd2e?= =?us-ascii?Q?ZU00n2Bjd6d4e4DI5sx0wViy5bIW9toQPTsi7h7AUfvspiDfChpc4juwh/Bx?= =?us-ascii?Q?CxmrLbDSY1ai5SOPXFDLFckQ9GJLrZRCYh8aOb/p/yCQZFdVhl6FOem/EHzC?= =?us-ascii?Q?hr0y0lCP+8IGivSHZ66kTaHmmSLuwFrwzFk1o75tTIctCk0YhIemQWo9F/EK?= =?us-ascii?Q?9bHo5C/Bl9qlIaAZHSGvN8BioWX3F1xekxVYK8CmtMmRJqn1AgSiQCnf3OPv?= =?us-ascii?Q?0d7ACHhXN/FTRLzs+81Z+4saFSj8VWNh0qfSBD1CrQNi/hGWn2foOr1iFodc?= =?us-ascii?Q?lTF6eXCzMI1UoLMXp35a1Cy22X4K/FtJhpOKtV1VgmAdVP8id5sPo6I2Rqb2?= =?us-ascii?Q?pe/ocMsZfgSLRXfuU02/W0NJJxgCHCHfZd5pAMF6khSHw96jP3HUTBoIp68P?= =?us-ascii?Q?jeRzan5hp8X5w/5Xzsrh0kv1Z9/ZIv+khaJQjU/43cmD6B+JLum6+RoMHQo3?= =?us-ascii?Q?LjPPQFDmMjYIcwRMjgaLIjjzheCGyEXo7Xt+y/ltxVe6XOPKM7NxdAabFN/F?= =?us-ascii?Q?bogakEbD8udJiDGLCnGnnivUji2rw2LzbDGbuHBrItFeSf13gpmQH3u4iawr?= =?us-ascii?Q?eW5DMAH/pfJ5c0zd21YGi91vBabZiqjcvf0bI1rFhe3FLzfpGd/YRh7TNOVl?= =?us-ascii?Q?VPq2VgG5QQFpY2F35geTeEQ4NcGda0bCRGdyiVR4PPzYkhh5Hjzxh1Km0ip0?= =?us-ascii?Q?9b8E9yhxws5bZbb0Vv6jOM2UFR4bMNpitM7X6ABxQd9K1Qv9Qz9Yg+vG7LjY?= =?us-ascii?Q?CfAFGU3PZfmWrjgp2Jf++/8xIr9bQMB+iNLQ2WAIofbSwGOPvQUvQw1YvrJG?= =?us-ascii?Q?orOkF0pin2lyypkQJ497VWl6tjfUjtcCEQnoaO8SMEPbNLSTkx2fcRWmYWg3?= =?us-ascii?Q?0s0LU25hkTZycpAqG00hEmZD6ecEZBIk6BxqL03q6iDWkFG0XteRVI5ep26C?= =?us-ascii?Q?h6ydJ5VtHoeH+QSw/H5N0+BTfp54RB2Cx8jFBaW1+J3MdFqQD+bOHN5q78wV?= =?us-ascii?Q?zUkc0CybizxFvz57osln+8rnZsBPE3nGD6CyvKO5pkhnf2u3X83I0jQcKz9a?= =?us-ascii?Q?lpaQ+n00boSO43h5UfG0cfPgLE6Kp0Wn2WkIPGAgrf/P3EcABfulV9xcDnVe?= =?us-ascii?Q?IZzdCaBL52+8ySGz1qxwF0mBuqRfcsaezYpeuWZiykXXrvoPbMKkWZMgRyPm?= =?us-ascii?Q?iaeXNGQMIb5T43X0KDrLgJjux/iqeqWsTWA5pu2an8Dye/Gi26/lv6V9u3J4?= =?us-ascii?Q?zGAAdlQbpqnwjDviNg3NlyEgQCs+rWoN+kD6KtieYuz/jxMrVEeHTASvJYpc?= =?us-ascii?Q?z90PYqZObw=3D=3D?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: ed61ac09-77db-4405-689c-08df1ed162b3 X-MS-Exchange-CrossTenant-AuthSource: DM6PR12MB4827.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Sep 2026 09:01:16.4079 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Wyx+tzzpUQ9suQEgS7Qxv8Fld3Fpn9p62gJ8idTKMNTtkTDHRkUMANQ/zUsqOTpc2TB5BcViqdKc5v/eICQnEA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH7PR12MB7817 Hierarchical BPF schedulers may need to know how many CPUs a cgroup can run on when distributing group-wide weights. For example, fair's group share calculation scales a group's weight by the smaller of its estimated runnable task count and the number of CPUs in its effective cpuset. Without that count, a BPF scheduler can only use the machine-wide CPU count and may give a group confined to a few CPUs excessive shares. A task's effective affinity can include per-task restrictions, so it cannot reliably represent the group's cpuset. Reading the cpuset directly from BPF would require CO-RE access to private cgroup and cpuset structures, including inherited cpuset resolution, making the approach fragile across kernel versions. Add scx_bpf_cgroup_nr_cpus(), which returns the same count fair uses through cpuset_num_cpus(). The count is independent of CPU or CID numbering, so the kfunc is available to both cpu-form and cid-form schedulers from any context. Also add a compat wrapper which falls back to nr_cpu_ids on older kernels. Signed-off-by: Andrea Righi --- kernel/sched/ext/ext.c | 18 ++++++++++++++++++ tools/sched_ext/include/scx/common.bpf.h | 1 + tools/sched_ext/include/scx/compat.bpf.h | 7 +++++++ 3 files changed, 26 insertions(+) diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c index 405d0d1038f82..e35f513876959 100644 --- a/kernel/sched/ext/ext.c +++ b/kernel/sched/ext/ext.c @@ -11355,6 +11355,23 @@ __bpf_kfunc struct cgroup *scx_bpf_task_cgroup(struct task_struct *p, cgroup_get(cgrp); return cgrp; } + +/** + * scx_bpf_cgroup_nr_cpus - Return the number of CPUs in a cgroup's cpuset + * @cgrp: cgroup of interest + * + * Return the number of CPUs in @cgrp's effective cpuset, which is inherited + * from the nearest ancestor with the cpuset controller enabled. This matches + * the count used by fair's group share calculation and lets hierarchical BPF + * schedulers bound a group's weight by the CPUs it can actually run on. + * + * The value is a snapshot and may change at any time through cpuset updates or + * CPU hotplug. Schedulers should re-read it when recomputing group state. + */ +__bpf_kfunc u32 scx_bpf_cgroup_nr_cpus(struct cgroup *cgrp) +{ + return cpuset_num_cpus(cgrp); +} #endif /* CONFIG_CGROUP_SCHED */ __bpf_kfunc_end_defs(); @@ -11402,6 +11419,7 @@ BTF_ID_FLAGS(func, scx_bpf_now) BTF_ID_FLAGS(func, scx_bpf_events, KF_IMPLICIT_ARGS) #ifdef CONFIG_CGROUP_SCHED BTF_ID_FLAGS(func, scx_bpf_task_cgroup, KF_IMPLICIT_ARGS | KF_RCU | KF_ACQUIRE) +BTF_ID_FLAGS(func, scx_bpf_cgroup_nr_cpus, KF_RCU) #endif BTF_ID_FLAGS(func, scx_bpf_sub_grant, KF_IMPLICIT_ARGS) BTF_ID_FLAGS(func, scx_bpf_sub_revoke, KF_IMPLICIT_ARGS) diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h index 5003e33f51423..28337ae8d9e66 100644 --- a/tools/sched_ext/include/scx/common.bpf.h +++ b/tools/sched_ext/include/scx/common.bpf.h @@ -104,6 +104,7 @@ struct task_struct *scx_bpf_cpu_curr(s32 cpu) __ksym __weak; struct task_struct *scx_bpf_tid_to_task(u64 tid) __ksym __weak; u64 scx_bpf_now(void) __ksym __weak; void scx_bpf_events(struct scx_event_stats *events, size_t events__sz) __ksym __weak; +u32 scx_bpf_cgroup_nr_cpus(struct cgroup *cgrp) __ksym __weak; s32 scx_bpf_cpu_to_cid(s32 cpu) __ksym __weak; s32 scx_bpf_cid_to_cpu(s32 cid) __ksym __weak; s32 scx_bpf_cid_node(s32 cid) __ksym __weak; diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h index c5c90d1d81e04..a793c5e8814b9 100644 --- a/tools/sched_ext/include/scx/compat.bpf.h +++ b/tools/sched_ext/include/scx/compat.bpf.h @@ -248,6 +248,13 @@ static inline bool __COMPAT_is_enq_cpu_selected(u64 enq_flags) (bpf_ksym_exists(scx_bpf_cid_node) ? \ scx_bpf_cid_node(cid) : NUMA_NO_NODE) +/* + * v7.4: Add scx_bpf_cgroup_nr_cpus(). + */ +#define __COMPAT_scx_bpf_cgroup_nr_cpus(cgrp) \ + (bpf_ksym_exists(scx_bpf_cgroup_nr_cpus) ? \ + scx_bpf_cgroup_nr_cpus(cgrp) : scx_bpf_nr_cpu_ids()) + /* * v6.18: Add a helper to retrieve the current task running on a CPU. * -- 2.55.0