linux-kernel - [PATCH v2 08/10] sched/deadline: Add support to remove DL server bandwidth

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Message-ID: <20250602180110.816225-9-joelagnelf@nvidia.com>
Date: Mon,  2 Jun 2025 14:01:04 -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 v2 08/10] sched/deadline: Add support to remove DL server bandwidth

The DL server for sched_ext will have its bandwidth removed when
sched_ext is unloaded. Add support to DEADLINE for this, so that the
sched_ext DL server may do so.

Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
---
 kernel/sched/deadline.c | 57 +++++++++++++++++++++++++++++++++++++++++
 kernel/sched/sched.h    |  1 +
 2 files changed, 58 insertions(+)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 4ed61266f3ea..e585ff39fcc3 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1752,6 +1752,63 @@ 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)
+{
+	struct rq *rq = dl_se->rq;
+	int cpu = cpu_of(rq);
+	struct dl_bw *dl_b;
+	int cpus;
+
+	if (!dl_se->dl_runtime)
+		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);
+
+	/* Cancel any pending timers */
+	hrtimer_try_to_cancel(&dl_se->dl_timer);
+	hrtimer_try_to_cancel(&dl_se->inactive_timer);
+
+	/* Remove bandwidth from both runqueue and root domain accounting */
+	dl_b = dl_bw_of(cpu);
+	guard(raw_spinlock)(&dl_b->lock);
+	cpus = dl_bw_cpus(cpu);
+	if (!cpus)
+		return 0;
+
+	sub_rq_bw(dl_se, &rq->dl);
+	__dl_sub(dl_b, dl_se->dl_bw, cpus);
+
+	/*
+	 * If server was active and consuming bandwidth, remove it from
+	 * running bandwidth accounting. This should not happen because
+	 * we call this only after the last dl_server_stop().
+	 */
+	if (WARN_ON_ONCE(!dl_se->dl_non_contending))
+		sub_running_bw(dl_se, &rq->dl);
+
+	/*
+	 * Clear all server parameters. This will also clear ->dl_server so
+	 * the next dl_server_apply_params() will reconfigure the server.
+	 */
+	__dl_clear_params(dl_se);
+
+	return 0;
+}
+
 /*
  * 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 d206421b1146..e6af0c1fc985 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