linux-kernel - [PATCH v4 10/15] sched/deadline: Add support to remove DLserver's bandwidth contribution

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Message-ID: <20250617200523.1261231-11-joelagnelf@nvidia.com>
Date: Tue, 17 Jun 2025 16:05:13 -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 v4 10/15] sched/deadline: Add support to remove DLserver's bandwidth contribution

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

During switching from sched_ext to FAIR tasks and vice-versa, we need
support for removing the bandwidth contribution of either DL server. Add
support for the same.

Co-developed-by: Joel Fernandes <joelagnelf@...dia.com>
Signed-off-by: Andrea Righi <arighi@...dia.com>
---
 kernel/sched/deadline.c | 31 +++++++++++++++++++++++++++++++
 kernel/sched/sched.h    |  1 +
 2 files changed, 32 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index c61752c2e052..50d938856b3d 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1742,6 +1742,12 @@ int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 perio
 		dl_rq_change_utilization(rq, dl_se, new_bw);
 	}
 
+	/* Clear these so that the dl_server is reinitialized */
+	if (new_bw == 0) {
+		dl_se->dl_defer = 0;
+		dl_se->dl_server = 0;
+	}
+
 	dl_se->dl_runtime = runtime;
 	dl_se->dl_deadline = period;
 	dl_se->dl_period = period;
@@ -1755,6 +1761,31 @@ int dl_server_apply_params(struct sched_dl_entity *dl_se, u64 runtime, u64 perio
 	return retval;
 }
 
+/**
+ * dl_server_remove_params - Remove bandwidth reservation for a DL server
+ * @dl_se: The DL server entity to remove bandwidth for
+ *
+ * This function removes the bandwidth reservation for a DL server entity,
+ * cleaning up all bandwidth accounting and server state.
+ *
+ * Returns: 0 on success, negative error code on failure
+ */
+int dl_server_remove_params(struct sched_dl_entity *dl_se)
+{
+	if (!dl_se->dl_server)
+		return 0; /* Already disabled */
+
+	/*
+	 * First dequeue if still queued. It should not be queued since
+	 * we call this only after the last dl_server_stop().
+	 */
+	if (WARN_ON_ONCE(on_dl_rq(dl_se)))
+		dequeue_dl_entity(dl_se, DEQUEUE_SLEEP);
+
+	/* Remove bandwidth reservation */
+	return dl_server_apply_params(dl_se, 0, dl_se->dl_period, false);
+}
+
 /*
  * Update the current task's runtime statistics (provided it is still
  * a -deadline task and has not been removed from the dl_rq).
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 576b69cee6b1..13dc32a6346a 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -393,6 +393,7 @@ 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_remove_params(struct sched_dl_entity *dl_se);
 
 static inline bool dl_server_active(struct sched_dl_entity *dl_se)
 {
-- 
2.43.0