[tip: sched/core] sched/deadline: Generalize unique visiting of root domains

[tip-bot2 for Juri Lelli]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     45007c6fb5860cf63556a9cadc87c8984927e23d
Gitweb:        https://git.kernel.org/tip/45007c6fb5860cf63556a9cadc87c8984927e23d
Author:        Juri Lelli <juri.lelli@xxxxxxxxxx>
AuthorDate:    Thu, 13 Mar 2025 18:05:46 +01:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 17 Mar 2025 11:23:41 +01:00

sched/deadline: Generalize unique visiting of root domains

Bandwidth checks and updates that work on root domains currently employ
a cookie mechanism for efficiency. This mechanism is very much tied to
when root domains are first created and initialized.

Generalize the cookie mechanism so that it can be used also later at
runtime while updating root domains. Also, additionally guard it with
sched_domains_mutex, since domains need to be stable while updating them
(and it will be required for further dynamic changes).

Fixes: 53916d5fd3c0 ("sched/deadline: Check bandwidth overflow earlier for hotplug")
Reported-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Valentin Schneider <vschneid@xxxxxxxxxx>
Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Tested-by: Waiman Long <longman@xxxxxxxxxx>
Tested-by: Jon Hunter <jonathanh@xxxxxxxxxx>
Tested-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
Link: https://lore.kernel.org/r/Z9MQaiXPvEeW_v7x@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
---
 include/linux/sched/deadline.h |  3 +++
 kernel/sched/deadline.c        | 23 +++++++++++++----------
 kernel/sched/rt.c              |  2 ++
 kernel/sched/sched.h           |  2 +-
 kernel/sched/topology.c        |  2 +-
 5 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/include/linux/sched/deadline.h b/include/linux/sched/deadline.h
index 3a912ab..6ec5786 100644
--- a/include/linux/sched/deadline.h
+++ b/include/linux/sched/deadline.h
@@ -37,4 +37,7 @@ extern void dl_clear_root_domain(struct root_domain *rd);
 
 #endif /* CONFIG_SMP */
 
+extern u64 dl_cookie;
+extern bool dl_bw_visited(int cpu, u64 cookie);
+
 #endif /* _LINUX_SCHED_DEADLINE_H */
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 1a041c1..3e05032 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -166,14 +166,14 @@ static inline unsigned long dl_bw_capacity(int i)
 	}
 }
 
-static inline bool dl_bw_visited(int cpu, u64 gen)
+static inline bool dl_bw_visited(int cpu, u64 cookie)
 {
 	struct root_domain *rd = cpu_rq(cpu)->rd;
 
-	if (rd->visit_gen == gen)
+	if (rd->visit_cookie == cookie)
 		return true;
 
-	rd->visit_gen = gen;
+	rd->visit_cookie = cookie;
 	return false;
 }
 
@@ -207,7 +207,7 @@ static inline unsigned long dl_bw_capacity(int i)
 	return SCHED_CAPACITY_SCALE;
 }
 
-static inline bool dl_bw_visited(int cpu, u64 gen)
+static inline bool dl_bw_visited(int cpu, u64 cookie)
 {
 	return false;
 }
@@ -3171,15 +3171,18 @@ DEFINE_SCHED_CLASS(dl) = {
 #endif
 };
 
-/* Used for dl_bw check and update, used under sched_rt_handler()::mutex */
-static u64 dl_generation;
+/*
+ * Used for dl_bw check and update, used under sched_rt_handler()::mutex and
+ * sched_domains_mutex.
+ */
+u64 dl_cookie;
 
 int sched_dl_global_validate(void)
 {
 	u64 runtime = global_rt_runtime();
 	u64 period = global_rt_period();
 	u64 new_bw = to_ratio(period, runtime);
-	u64 gen = ++dl_generation;
+	u64 cookie = ++dl_cookie;
 	struct dl_bw *dl_b;
 	int cpu, cpus, ret = 0;
 	unsigned long flags;
@@ -3192,7 +3195,7 @@ int sched_dl_global_validate(void)
 	for_each_online_cpu(cpu) {
 		rcu_read_lock_sched();
 
-		if (dl_bw_visited(cpu, gen))
+		if (dl_bw_visited(cpu, cookie))
 			goto next;
 
 		dl_b = dl_bw_of(cpu);
@@ -3229,7 +3232,7 @@ static void init_dl_rq_bw_ratio(struct dl_rq *dl_rq)
 void sched_dl_do_global(void)
 {
 	u64 new_bw = -1;
-	u64 gen = ++dl_generation;
+	u64 cookie = ++dl_cookie;
 	struct dl_bw *dl_b;
 	int cpu;
 	unsigned long flags;
@@ -3240,7 +3243,7 @@ void sched_dl_do_global(void)
 	for_each_possible_cpu(cpu) {
 		rcu_read_lock_sched();
 
-		if (dl_bw_visited(cpu, gen)) {
+		if (dl_bw_visited(cpu, cookie)) {
 			rcu_read_unlock_sched();
 			continue;
 		}
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 4b8e33c..8cebe71 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2910,6 +2910,7 @@ static int sched_rt_handler(const struct ctl_table *table, int write, void *buff
 	int ret;
 
 	mutex_lock(&mutex);
+	sched_domains_mutex_lock();
 	old_period = sysctl_sched_rt_period;
 	old_runtime = sysctl_sched_rt_runtime;
 
@@ -2936,6 +2937,7 @@ undo:
 		sysctl_sched_rt_period = old_period;
 		sysctl_sched_rt_runtime = old_runtime;
 	}
+	sched_domains_mutex_unlock();
 	mutex_unlock(&mutex);
 
 	return ret;
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e8915ad..5d853f9 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -998,7 +998,7 @@ struct root_domain {
 	 * Also, some corner cases, like 'wrap around' is dangerous, but given
 	 * that u64 is 'big enough'. So that shouldn't be a concern.
 	 */
-	u64 visit_gen;
+	u64 visit_cookie;
 
 #ifdef HAVE_RT_PUSH_IPI
 	/*
diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
index 296ff2a..4409333 100644
--- a/kernel/sched/topology.c
+++ b/kernel/sched/topology.c
@@ -568,7 +568,7 @@ static int init_rootdomain(struct root_domain *rd)
 	rd->rto_push_work = IRQ_WORK_INIT_HARD(rto_push_irq_work_func);
 #endif
 
-	rd->visit_gen = 0;
+	rd->visit_cookie = 0;
 	init_dl_bw(&rd->dl_bw);
 	if (cpudl_init(&rd->cpudl) != 0)
 		goto free_rto_mask;