[PATCH 02/11] sched/debug: Stop and start server based on if it was active

Andrea Righi
2025-10-29T19:11:45Z

From: Joel Fernandes <joelagnelf@nvidia.com>

Currently the DL server interface for applying parameters checks
CFS-internals to identify if the server is active. This is error-prone
and makes it difficult when adding new servers in the future.

Fix it, by using dl_server_active() which is also used by the DL server
code to determine if the DL server was started.

Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Juri Lelli <juri.lelli@redhat.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Joel Fernandes <joelagnelf@nvidia.com>
---
kernel/sched/debug.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 6cf9be6eea49a..e71f6618c1a6a 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -354,6 +354,8 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
return err;

scoped_guard (rq_lock_irqsave, rq) {
+ bool is_active;
+
runtime = rq->fair_server.dl_runtime;
period = rq->fair_server.dl_period;

@@ -376,8 +378,11 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
return -EINVAL;
}

- update_rq_clock(rq);
- dl_server_stop(&rq->fair_server);
+ is_active = dl_server_active(&rq->fair_server);
+ if (is_active) {
+ update_rq_clock(rq);
+ dl_server_stop(&rq->fair_server);
+ }

retval = dl_server_apply_params(&rq->fair_server, runtime, period, 0);

@@ -385,7 +390,7 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
printk_deferred("Fair server disabled in CPU %d, system may crash due to starvation.\n",
cpu_of(rq));

- if (rq->cfs.h_nr_queued)
+ if (is_active)
dl_server_start(&rq->fair_server);

if (retval < 0)
--
2.51.2