linux-kernel - [RFC][PATCH v0.1 5/6] sched/topology: Allow .setpolicy() cpufreq drivers to enable EAS

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Message-ID: <1889415.atdPhlSkOF@rjwysocki.net>
Date: Fri, 08 Nov 2024 17:41:22 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, Lukasz Luba <lukasz.luba@....com>,
 Peter Zijlstra <peterz@...radead.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
 Len Brown <len.brown@...el.com>, Dietmar Eggemann <dietmar.eggemann@....com>,
 Morten Rasmussen <morten.rasmussen@....com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject:
 [RFC][PATCH v0.1 5/6] sched/topology: Allow .setpolicy() cpufreq drivers to
 enable EAS

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Some cpufreq drivers, like intel_pstate, have built-in governors that
are used instead of regular cpufreq governors, schedutil in particular,
but they can work with EAS just fine, so allow EAS to be used with
those drivers.

Also update the debug message printed when the cpufreq governor in
use is not schedutil and the related comment, to better match the
code after the change.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---

I'm not sure how much value there is in refusing to enable EAS without
schedutil in general.  For instance, if there are no crossover points
between the cost curves for different perf domains, EAS may as well be
used with the performance and powersave governors AFAICS.

---
 kernel/sched/topology.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

Index: linux-pm/kernel/sched/topology.c
===================================================================
--- linux-pm.orig/kernel/sched/topology.c
+++ linux-pm/kernel/sched/topology.c
@@ -251,7 +251,7 @@ static bool sched_is_eas_possible(const
 		return false;
 	}

-	/* Do not attempt EAS if schedutil is not being used. */
+	/* Do not attempt EAS with a cpufreq governor other than schedutil. */
 	for_each_cpu(i, cpu_mask) {
 		policy = cpufreq_cpu_get(i);
 		if (!policy) {
@@ -263,9 +263,9 @@ static bool sched_is_eas_possible(const
 		}
 		gov = policy->governor;
 		cpufreq_cpu_put(policy);
-		if (gov != &schedutil_gov) {
+		if (gov && gov != &schedutil_gov) {
 			if (sched_debug()) {
-				pr_info("rd %*pbl: Checking EAS, schedutil is mandatory\n",
+				pr_info("rd %*pbl: Checking EAS, cpufreq governor is not schedutil\n",
 					cpumask_pr_args(cpu_mask));
 			}
 			return false;