[PATCH 27/31] sched_ext: Implement sched_ext_ops.cpu_online/offline()

[Tejun Heo]

Add ops.cpu_online/offline() which are invoked when CPUs come online and
offline respectively. As the enqueue path already automatically bypasses
tasks to the local dsq on a deactivated CPU, BPF schedulers are guaranteed
to see tasks only on CPUs which are between online() and offline().

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-by: David Vernet <dvernet@xxxxxxxx>
Acked-by: Josh Don <joshdon@xxxxxxxxxx>
Acked-by: Hao Luo <haoluo@xxxxxxxxxx>
Acked-by: Barret Rhoden <brho@xxxxxxxxxx>
---
 include/linux/sched/ext.h | 18 ++++++++++++++++++
 kernel/sched/ext.c        | 15 +++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 61f45aa03704..d9f941e23011 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -384,6 +384,24 @@ struct sched_ext_ops {
 	 */
 	void (*cpu_release)(s32 cpu, struct scx_cpu_release_args *args);
 
+	/**
+	 * cpu_online - A CPU became online
+	 * @cpu: CPU which just came up
+	 *
+	 * @cpu just came online. @cpu doesn't call ->enqueue() or consume tasks
+	 * associated with other CPUs beforehand.
+	 */
+	void (*cpu_online)(s32 cpu);
+
+	/**
+	 * cpu_offline - A CPU is going offline
+	 * @cpu: CPU which is going offline
+	 *
+	 * @cpu is going offline. @cpu doesn't call ->enqueue() or consume tasks
+	 * associated with other CPUs afterwards.
+	 */
+	void (*cpu_offline)(s32 cpu);
+
 	/**
 	 * prep_enable - Prepare to enable BPF scheduling for a task
 	 * @p: task to prepare BPF scheduling for
diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 9a7a4e54e8fa..aab9ae13b88f 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -1574,6 +1574,18 @@ void __scx_update_idle(struct rq *rq, bool idle)
 	}
 }
 
+static void rq_online_scx(struct rq *rq, enum rq_onoff_reason reason)
+{
+	if (SCX_HAS_OP(cpu_online) && reason == RQ_ONOFF_HOTPLUG)
+		scx_ops.cpu_online(cpu_of(rq));
+}
+
+static void rq_offline_scx(struct rq *rq, enum rq_onoff_reason reason)
+{
+	if (SCX_HAS_OP(cpu_offline) && reason == RQ_ONOFF_HOTPLUG)
+		scx_ops.cpu_offline(cpu_of(rq));
+}
+
 #else /* !CONFIG_SMP */
 
 static bool test_and_clear_cpu_idle(int cpu) { return false; }
@@ -2049,6 +2061,9 @@ DEFINE_SCHED_CLASS(ext) = {
 	.pick_task		= pick_task_scx,
 
 	.set_cpus_allowed	= set_cpus_allowed_scx,
+
+	.rq_online		= rq_online_scx,
+	.rq_offline		= rq_offline_scx,
 #endif
 
 	.task_tick		= task_tick_scx,
-- 
2.38.1