linux-kernel - [PATCH RFC 5/8] sched/debug: Stop and start server based on if it was active

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Message-ID: <20250315022158.2354454-6-joelagnelf@nvidia.com>
Date: Fri, 14 Mar 2025 22:21:52 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: linux-kernel@...r.kernel.org,
	Andrea Righi <arighi@...dia.com>,
	Tejun Heo <tj@...nel.org>,
	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>
Cc: Luigi De Matteis <ldematteis123@...il.com>,
	paulmck@...nel.org,
	boqun.feng@...il.com,
	David Vernet <void@...ifault.com>,
	Joel Fernandes <joelagnelf@...dia.com>
Subject: [PATCH RFC 5/8] sched/debug: Stop and start server based on if it was active

Currently the DL server interface for applying parameters checkfs
CFS-internals to identify if the server is active. This is error-prone
and make 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.

Reviewed-by: Andrea Righi <arighi@...dia.com>
Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
---
 kernel/sched/debug.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 1ccc7687e1a8..83cb695d6d46 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -347,6 +347,7 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 {
 	long cpu = (long) ((struct seq_file *) filp->private_data)->private;
 	struct rq *rq = cpu_rq(cpu);
+	bool was_active = false;
 	u64 runtime, period;
 	int retval = 0;
 	size_t err;
@@ -379,7 +380,8 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
 			return  -EINVAL;
 		}
 
-		if (rq->cfs.h_nr_queued) {
+		if (dl_server_active(&rq->fair_server)) {
+			was_active = true;
 			update_rq_clock(rq);
 			dl_server_stop(&rq->fair_server);
 		}
@@ -390,7 +392,7 @@ 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 (was_active)
 			dl_server_start(&rq->fair_server);
 
 		if (retval < 0)
-- 
2.43.0