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Subject[RFC/RFT][PATCH 1/2] cpufreq: schedutil: Use policy-dependent latency multupliers
Date
From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Make the schedutil governor compute the initial (default) value of
the rate_limit_us sysfs attribute by multiplying the transition
latency by a multiplier depending on the policy and set by the
scaling driver (instead of using a constant for this purpose).

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 use the opportunity to reduce the rate limit
somewhat.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
drivers/cpufreq/cpufreq.c | 1 +
drivers/cpufreq/intel_pstate.c | 2 ++
include/linux/cpufreq.h | 8 ++++++++
kernel/sched/cpufreq_schedutil.c | 2 +-
4 files changed, 12 insertions(+), 1 deletion(-)

Index: linux-pm/drivers/cpufreq/cpufreq.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/cpufreq.c
+++ linux-pm/drivers/cpufreq/cpufreq.c
@@ -1072,6 +1072,7 @@ static struct cpufreq_policy *cpufreq_po
init_waitqueue_head(&policy->transition_wait);
init_completion(&policy->kobj_unregister);
INIT_WORK(&policy->update, handle_update);
+ policy->latency_multiplier = LATENCY_MULTIPLIER;

policy->cpu = cpu;
return policy;
Index: linux-pm/include/linux/cpufreq.h
===================================================================
--- linux-pm.orig/include/linux/cpufreq.h
+++ linux-pm/include/linux/cpufreq.h
@@ -120,6 +120,14 @@ struct cpufreq_policy {
bool fast_switch_possible;
bool fast_switch_enabled;

+ /*
+ * Multiplier to apply to the transition latency to obtain the preferred
+ * average time interval between consecutive invocations of the driver
+ * to set the frequency for this policy. Initialized by the core to the
+ * LATENCY_MULTIPLIER value.
+ */
+ unsigned int latency_multiplier;
+
/* 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
@@ -530,7 +530,7 @@ static int sugov_init(struct cpufreq_pol
goto stop_kthread;
}

- tunables->rate_limit_us = LATENCY_MULTIPLIER;
+ tunables->rate_limit_us = policy->latency_multiplier;
lat = policy->cpuinfo.transition_latency / NSEC_PER_USEC;
if (lat)
tunables->rate_limit_us *= lat;
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_LATENCY_MULTIPLIER 250

#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->latency_multiplier = INTEL_CPUFREQ_LATENCY_MULTIPLIER;
/* This reflects the intel_pstate_get_cpu_pstates() setting. */
policy->cur = policy->cpuinfo.min_freq;

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