linux-kernel - [PATCH] cpufreq/schedutil: Only bind threads if needed

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Message-ID: <5a8deed4-7764-4729-a9d4-9520c25fa7e8@arm.com>
Date: Mon, 20 Jan 2025 10:09:46 +0000
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc: 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>,
 linux-pm <linux-pm@...r.kernel.org>
Subject: [PATCH] cpufreq/schedutil: Only bind threads if needed

Remove the unconditional binding of sugov kthreads to the affected CPUs
if the cpufreq driver indicates that updates can happen from any CPU.
This allows userspace to set affinities to either save power (waking up
bigger CPUs on HMP can be expensive) or increasing performance (by
letting the utilized CPUs run without preemption of the sugov kthread).

Signed-off-by: Christian Loehle <christian.loehle@....com>
Acked-by: Viresh Kumar <viresh.kumar@...aro.org>
Acked-by: Vincent Guittot <vincent.guittot@...aro.org>
Acked-by: Rafael J. Wysocki <rafael@...nel.org>
Acked-by: Juri Lelli <juri.lelli@...hat.com>
---
- RESEND: pick up tags
- v2: Add comment for the dl_task_check_affinity return (Juri)
v2: https://lore.kernel.org/lkml/a4a70646-98a4-4b85-955e-62d66ba68927@arm.com/
v1: https://lore.kernel.org/lkml/480f2140-ea59-4e1d-a68d-18cbcec10941@arm.com/

 kernel/sched/cpufreq_schedutil.c | 6 +++++-
 kernel/sched/syscalls.c          | 7 +++++++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c
index 28c77904ea74..a81444501158 100644
--- a/kernel/sched/cpufreq_schedutil.c
+++ b/kernel/sched/cpufreq_schedutil.c
@@ -691,7 +691,11 @@ static int sugov_kthread_create(struct sugov_policy *sg_policy)
 	}

 	sg_policy->thread = thread;
-	kthread_bind_mask(thread, policy->related_cpus);
+	if (policy->dvfs_possible_from_any_cpu)
+		set_cpus_allowed_ptr(thread, policy->related_cpus);
+	else
+		kthread_bind_mask(thread, policy->related_cpus);
+
 	init_irq_work(&sg_policy->irq_work, sugov_irq_work);
 	mutex_init(&sg_policy->work_lock);

diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index ff0e5ab4e37c..8230358d2b90 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -1139,6 +1139,13 @@ int dl_task_check_affinity(struct task_struct *p, const struct cpumask *mask)
 	if (!task_has_dl_policy(p) || !dl_bandwidth_enabled())
 		return 0;

+	/*
+	 * The special/sugov task isn't part of regular bandwidth/admission
+	 * control so let userspace change affinities.
+	 */
+	if (dl_entity_is_special(&p->dl))
+		return 0;
+
 	/*
 	 * Since bandwidth control happens on root_domain basis,
 	 * if admission test is enabled, we only admit -deadline
-- 
2.34.1