linux-kernel - [PATCH -rebased 11/15] sched/deadline: Allow to initialize DL server when needed

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Message-Id: <20250809184800.129831-12-joelagnelf@nvidia.com>
Date: Sat,  9 Aug 2025 14:47:56 -0400
From: Joel Fernandes <joelagnelf@...dia.com>
To: linux-kernel@...r.kernel.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: Joel Fernandes <joelagnelf@...dia.com>,
	Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Andrea Righi <arighi@...dia.com>,
	Changwoo Min <changwoo@...lia.com>
Subject: [PATCH -rebased 11/15] sched/deadline: Allow to initialize DL server when needed

From: Andrea Righi <arighi@...dia.com>

When switching between fair and sched_ext, we need to initialize the
bandwidth contribution of the DL server independently for each class.

Add support for on-demand initialization to handle such transitions.

Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 kernel/sched/deadline.c | 36 +++++++++++++++++++++++++++++-------
 kernel/sched/sched.h    |  1 +
 2 files changed, 30 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 92ca2f5b7cb9..7891a7bf43d6 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1583,6 +1583,32 @@ void dl_server_update(struct sched_dl_entity *dl_se, s64 delta_exec)
 	}
 }
 
+/**
+ * dl_server_init_params - Initialize bandwidth reservation for a DL server
+ * @dl_se: The DL server entity to remove bandwidth for
+ *
+ * This function initializes the bandwidth reservation for a DL server
+ * entity, its bandwidth accounting and server state.
+ *
+ * Returns: 0 on success, negative error code on failure
+ */
+int dl_server_init_params(struct sched_dl_entity *dl_se)
+{
+	u64 runtime =  50 * NSEC_PER_MSEC;
+	u64 period = 1000 * NSEC_PER_MSEC;
+	int err;
+
+	err = dl_server_apply_params(dl_se, runtime, period, 1);
+	if (err)
+		return err;
+
+	dl_se->dl_server = 1;
+	dl_se->dl_defer = 1;
+	setup_new_dl_entity(dl_se);
+
+	return err;
+}
+
 void dl_server_start(struct sched_dl_entity *dl_se)
 {
 	struct rq *rq = dl_se->rq;
@@ -1638,8 +1664,7 @@ void sched_init_dl_servers(void)
 	struct sched_dl_entity *dl_se;
 
 	for_each_online_cpu(cpu) {
-		u64 runtime =  50 * NSEC_PER_MSEC;
-		u64 period = 1000 * NSEC_PER_MSEC;
+		int err;
 
 		rq = cpu_rq(cpu);
 
@@ -1649,11 +1674,8 @@ void sched_init_dl_servers(void)
 
 		WARN_ON(dl_server(dl_se));
 
-		dl_server_apply_params(dl_se, runtime, period, 1);
-
-		dl_se->dl_server = 1;
-		dl_se->dl_defer = 1;
-		setup_new_dl_entity(dl_se);
+		err = dl_server_init_params(dl_se);
+		WARN_ON_ONCE(err);
 	}
 }
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 719f9424b417..fe587b3bb88a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -395,6 +395,7 @@ extern void ext_server_init(struct rq *rq);
 extern void __dl_server_attach_root(struct sched_dl_entity *dl_se, struct rq *rq);
 extern int dl_server_apply_params(struct sched_dl_entity *dl_se,
 		    u64 runtime, u64 period, bool init);
+extern int dl_server_init_params(struct sched_dl_entity *dl_se);
 extern int dl_server_remove_params(struct sched_dl_entity *dl_se);
 
 static inline bool dl_server_active(struct sched_dl_entity *dl_se)
-- 
2.34.1