cpufreq: ondemand: Change the calculation of target frequency
The ondemand governor calculates load in terms of frequency and
increases it only if load_freq is greater than up_threshold
multiplied by the current or average frequency. This appears to
produce oscillations of frequency between min and max because,
for example, a relatively small load can easily saturate minimum
frequency and lead the CPU to the max. Then, it will decrease
back to the min due to small load_freq.
Change the calculation method of load and target frequency on the
basis of the following two observations:
- Load computation should not depend on the current or average
measured frequency. For example, absolute load of 80% at 100MHz
is not necessarily equivalent to 8% at 1000MHz in the next
sampling interval.
- It should be possible to increase the target frequency to any
value present in the frequency table proportional to the absolute
load, rather than to the max only, so that:
Target frequency = C * load
where we take C = policy->cpuinfo.max_freq / 100.
Tested on Intel i7-3770 CPU @ 3.40GHz and on Quad core 1500MHz Krait.
Phoronix benchmark of Linux Kernel Compilation 3.1 test shows an
increase ~1.5% in performance. cpufreq_stats (time_in_state) shows
that middle frequencies are used more, with this patch. Highest
and lowest frequencies were used less by ~9%.
[rjw: We have run multiple other tests on kernels with this
change applied and in the vast majority of cases it turns out
that the resulting performance improvement also leads to reduced
consumption of energy. The change is additionally justified by
the overall simplification of the code in question.]
Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 93eb5cb..a3c5574 100644
--- a/drivers/cpufreq/cpufreq_ondemand.c
+++ b/drivers/cpufreq/cpufreq_ondemand.c
@@ -29,11 +29,9 @@
#include "cpufreq_governor.h"
/* On-demand governor macros */
-#define DEF_FREQUENCY_DOWN_DIFFERENTIAL (10)
#define DEF_FREQUENCY_UP_THRESHOLD (80)
#define DEF_SAMPLING_DOWN_FACTOR (1)
#define MAX_SAMPLING_DOWN_FACTOR (100000)
-#define MICRO_FREQUENCY_DOWN_DIFFERENTIAL (3)
#define MICRO_FREQUENCY_UP_THRESHOLD (95)
#define MICRO_FREQUENCY_MIN_SAMPLE_RATE (10000)
#define MIN_FREQUENCY_UP_THRESHOLD (11)
@@ -161,14 +159,10 @@
/*
* Every sampling_rate, we check, if current idle time is less than 20%
- * (default), then we try to increase frequency. Every sampling_rate, we look
- * for the lowest frequency which can sustain the load while keeping idle time
- * over 30%. If such a frequency exist, we try to decrease to this frequency.
- *
- * Any frequency increase takes it to the maximum frequency. Frequency reduction
- * happens at minimum steps of 5% (default) of current frequency
+ * (default), then we try to increase frequency. Else, we adjust the frequency
+ * proportional to load.
*/
-static void od_check_cpu(int cpu, unsigned int load_freq)
+static void od_check_cpu(int cpu, unsigned int load)
{
struct od_cpu_dbs_info_s *dbs_info = &per_cpu(od_cpu_dbs_info, cpu);
struct cpufreq_policy *policy = dbs_info->cdbs.cur_policy;
@@ -178,29 +172,17 @@
dbs_info->freq_lo = 0;
/* Check for frequency increase */
- if (load_freq > od_tuners->up_threshold * policy->cur) {
+ if (load > od_tuners->up_threshold) {
/* If switching to max speed, apply sampling_down_factor */
if (policy->cur < policy->max)
dbs_info->rate_mult =
od_tuners->sampling_down_factor;
dbs_freq_increase(policy, policy->max);
return;
- }
-
- /* Check for frequency decrease */
- /* if we cannot reduce the frequency anymore, break out early */
- if (policy->cur == policy->min)
- return;
-
- /*
- * The optimal frequency is the frequency that is the lowest that can
- * support the current CPU usage without triggering the up policy. To be
- * safe, we focus 10 points under the threshold.
- */
- if (load_freq < od_tuners->adj_up_threshold
- * policy->cur) {
+ } else {
+ /* Calculate the next frequency proportional to load */
unsigned int freq_next;
- freq_next = load_freq / od_tuners->adj_up_threshold;
+ freq_next = load * policy->cpuinfo.max_freq / 100;
/* No longer fully busy, reset rate_mult */
dbs_info->rate_mult = 1;
@@ -374,9 +356,6 @@
input < MIN_FREQUENCY_UP_THRESHOLD) {
return -EINVAL;
}
- /* Calculate the new adj_up_threshold */
- od_tuners->adj_up_threshold += input;
- od_tuners->adj_up_threshold -= od_tuners->up_threshold;
od_tuners->up_threshold = input;
return count;
@@ -525,8 +504,6 @@
if (idle_time != -1ULL) {
/* Idle micro accounting is supported. Use finer thresholds */
tuners->up_threshold = MICRO_FREQUENCY_UP_THRESHOLD;
- tuners->adj_up_threshold = MICRO_FREQUENCY_UP_THRESHOLD -
- MICRO_FREQUENCY_DOWN_DIFFERENTIAL;
/*
* In nohz/micro accounting case we set the minimum frequency
* not depending on HZ, but fixed (very low). The deferred
@@ -535,8 +512,6 @@
dbs_data->min_sampling_rate = MICRO_FREQUENCY_MIN_SAMPLE_RATE;
} else {
tuners->up_threshold = DEF_FREQUENCY_UP_THRESHOLD;
- tuners->adj_up_threshold = DEF_FREQUENCY_UP_THRESHOLD -
- DEF_FREQUENCY_DOWN_DIFFERENTIAL;
/* For correct statistics, we need 10 ticks for each measure */
dbs_data->min_sampling_rate = MIN_SAMPLING_RATE_RATIO *