[RFC/RFT][PATCH 1/2] cpufreq: schedutil: Use policy-dependent transition delays

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

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

Make the schedutil governor take the initial (default) value of the
rate_limit_us sysfs attribute from the (new) transition_delay_us
policy parameter (to be set by the scaling driver).

That will allow scaling drivers to make schedutil use smaller default
values of rate_limit_us and reduce the default average time interval
between consecutive frequency changes.

Make intel_pstate set transition_delay_us to 500.

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

This is a replacement for https://patchwork.kernel.org/patch/9671831/

---
 drivers/cpufreq/intel_pstate.c   |    2 ++
 include/linux/cpufreq.h          |    7 +++++++
 kernel/sched/cpufreq_schedutil.c |   15 ++++++++++-----
 3 files changed, 19 insertions(+), 5 deletions(-)

Index: linux-pm/include/linux/cpufreq.h
===================================================================
--- linux-pm.orig/include/linux/cpufreq.h
+++ linux-pm/include/linux/cpufreq.h
@@ -120,6 +120,13 @@ struct cpufreq_policy {
 	bool			fast_switch_possible;
 	bool			fast_switch_enabled;
 
+	/*
+	 * Preferred average time interval between consecutive invocations of
+	 * the driver to set the frequency for this policy.  To be set by the
+	 * scaling driver (0, which is the default, means no preference).
+	 */
+	unsigned int		transition_delay_us;
+
 	 /* Cached frequency lookup from cpufreq_driver_resolve_freq. */
 	unsigned int cached_target_freq;
 	int cached_resolved_idx;
Index: linux-pm/kernel/sched/cpufreq_schedutil.c
===================================================================
--- linux-pm.orig/kernel/sched/cpufreq_schedutil.c
+++ linux-pm/kernel/sched/cpufreq_schedutil.c
@@ -491,7 +491,6 @@ static int sugov_init(struct cpufreq_pol
 {
 	struct sugov_policy *sg_policy;
 	struct sugov_tunables *tunables;
-	unsigned int lat;
 	int ret = 0;
 
 	/* State should be equivalent to EXIT */
@@ -530,10 +529,16 @@ static int sugov_init(struct cpufreq_pol
 		goto stop_kthread;
 	}
 
-	tunables->rate_limit_us = LATENCY_MULTIPLIER;
-	lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
-	if (lat)
-		tunables->rate_limit_us *= lat;
+	if (policy->transition_delay_us) {
+		tunables->rate_limit_us = policy->transition_delay_us;
+	} else {
+		unsigned int lat;
+
+		tunables->rate_limit_us = LATENCY_MULTIPLIER;
+		lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
+		if (lat)
+			tunables->rate_limit_us *= lat;
+	}
 
 	policy->governor_data = sg_policy;
 	sg_policy->tunables = tunables;
Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -41,6 +41,7 @@
 #define INTEL_PSTATE_HWP_SAMPLING_INTERVAL	(50 * NSEC_PER_MSEC)
 
 #define INTEL_CPUFREQ_TRANSITION_LATENCY	20000
+#define INTEL_CPUFREQ_TRANSITION_DELAY		500
 
 #ifdef CONFIG_ACPI
 #include <acpi/processor.h>
@@ -2237,6 +2238,7 @@ static int intel_cpufreq_cpu_init(struct
 		return ret;
 
 	policy->cpuinfo.transition_latency = INTEL_CPUFREQ_TRANSITION_LATENCY;
+	policy->transition_delay_us = INTEL_CPUFREQ_TRANSITION_DELAY;
 	/* This reflects the intel_pstate_get_cpu_pstates() setting. */
 	policy->cur = policy->cpuinfo.min_freq;