This is a note to let you know that I've just added the patch titled
sched/deadline: Correctly account for allocated bandwidth during hotplug
to the 6.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-deadline-correctly-account-for-allocated-bandw.patch
and it can be found in the queue-6.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4a75049f87443321e24f1cfc4f168e1d8512898c
Author: Juri Lelli <juri.lelli@xxxxxxxxxx>
Date: Thu Nov 14 14:28:10 2024 +0000
sched/deadline: Correctly account for allocated bandwidth during hotplug
[ Upstream commit d4742f6ed7ea6df56e381f82ba4532245fa1e561 ]
For hotplug operations, DEADLINE needs to check that there is still enough
bandwidth left after removing the CPU that is going offline. We however
fail to do so currently.
Restore the correct behavior by restructuring dl_bw_manage() a bit, so
that overflow conditions (not enough bandwidth left) are properly
checked. Also account for dl_server bandwidth, i.e. discount such
bandwidth in the calculation since NORMAL tasks will be anyway moved
away from the CPU as a result of the hotplug operation.
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>
Tested-by: Waiman Long <longman@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20241114142810.794657-3-juri.lelli@xxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ffceb5ff4c5c3..141bbe97d7e5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -8185,7 +8185,7 @@ static void cpuset_cpu_active(void)
static int cpuset_cpu_inactive(unsigned int cpu)
{
if (!cpuhp_tasks_frozen) {
- int ret = dl_bw_check_overflow(cpu);
+ int ret = dl_bw_deactivate(cpu);
if (ret)
return ret;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index d94f2ed6d1f46..b078014273d9e 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -3453,29 +3453,31 @@ int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur,
}
enum dl_bw_request {
- dl_bw_req_check_overflow = 0,
+ dl_bw_req_deactivate = 0,
dl_bw_req_alloc,
dl_bw_req_free
};
static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw)
{
- unsigned long flags;
+ unsigned long flags, cap;
struct dl_bw *dl_b;
bool overflow = 0;
+ u64 fair_server_bw = 0;
rcu_read_lock_sched();
dl_b = dl_bw_of(cpu);
raw_spin_lock_irqsave(&dl_b->lock, flags);
- if (req == dl_bw_req_free) {
+ cap = dl_bw_capacity(cpu);
+ switch (req) {
+ case dl_bw_req_free:
__dl_sub(dl_b, dl_bw, dl_bw_cpus(cpu));
- } else {
- unsigned long cap = dl_bw_capacity(cpu);
-
+ break;
+ case dl_bw_req_alloc:
overflow = __dl_overflow(dl_b, cap, 0, dl_bw);
- if (req == dl_bw_req_alloc && !overflow) {
+ if (!overflow) {
/*
* We reserve space in the destination
* root_domain, as we can't fail after this point.
@@ -3484,6 +3486,34 @@ static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw)
*/
__dl_add(dl_b, dl_bw, dl_bw_cpus(cpu));
}
+ break;
+ case dl_bw_req_deactivate:
+ /*
+ * cpu is going offline and NORMAL tasks will be moved away
+ * from it. We can thus discount dl_server bandwidth
+ * contribution as it won't need to be servicing tasks after
+ * the cpu is off.
+ */
+ if (cpu_rq(cpu)->fair_server.dl_server)
+ fair_server_bw = cpu_rq(cpu)->fair_server.dl_bw;
+
+ /*
+ * Not much to check if no DEADLINE bandwidth is present.
+ * dl_servers we can discount, as tasks will be moved out the
+ * offlined CPUs anyway.
+ */
+ if (dl_b->total_bw - fair_server_bw > 0) {
+ /*
+ * Leaving at least one CPU for DEADLINE tasks seems a
+ * wise thing to do.
+ */
+ if (dl_bw_cpus(cpu))
+ overflow = __dl_overflow(dl_b, cap, fair_server_bw, 0);
+ else
+ overflow = 1;
+ }
+
+ break;
}
raw_spin_unlock_irqrestore(&dl_b->lock, flags);
@@ -3492,9 +3522,9 @@ static int dl_bw_manage(enum dl_bw_request req, int cpu, u64 dl_bw)
return overflow ? -EBUSY : 0;
}
-int dl_bw_check_overflow(int cpu)
+int dl_bw_deactivate(int cpu)
{
- return dl_bw_manage(dl_bw_req_check_overflow, cpu, 0);
+ return dl_bw_manage(dl_bw_req_deactivate, cpu, 0);
}
int dl_bw_alloc(int cpu, u64 dl_bw)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index c5d67a43fe524..96d9bbba94acc 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -362,7 +362,7 @@ extern void __getparam_dl(struct task_struct *p, struct sched_attr *attr);
extern bool __checkparam_dl(const struct sched_attr *attr);
extern bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr);
extern int dl_cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
-extern int dl_bw_check_overflow(int cpu);
+extern int dl_bw_deactivate(int cpu);
extern s64 dl_scaled_delta_exec(struct rq *rq, struct sched_dl_entity *dl_se, s64 delta_exec);
/*
* SCHED_DEADLINE supports servers (nested scheduling) with the following
