linux-kernel - [PATCH 02/14] sched/debug: Stop and start server based on if it was active

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Message-ID: <20251017093214.70029-3-arighi@nvidia.com>
Date: Fri, 17 Oct 2025 11:25:49 +0200
From: Andrea Righi <arighi@...dia.com>
To: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joelagnelf@...dia.com>,
	Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>,
	Shuah Khan <shuah@...nel.org>
Cc: sched-ext@...ts.linux.dev,
	bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 02/14] sched/debug: Stop and start server based on if it was active

From: Joel Fernandes <joelagnelf@...dia.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@...nel.org>
Reviewed-by: Andrea Righi <arighi@...dia.com>
Signed-off-by: Joel Fernandes <joelagnelf@...dia.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)
-- 
2.51.0