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Message-ID: <51A4E357.5020509@semaphore.gr>
Date: Tue, 28 May 2013 20:03:19 +0300
From: Stratos Karafotis <stratosk@...aphore.gr>
To: "Rafael J. Wysocki" <rjw@...k.pl>
CC: Viresh Kumar <viresh.kumar@...aro.org>, cpufreq@...r.kernel.org,
linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] cpufreq: ondemand: Increase frequency to any value
proportional to load
Hi Rafael,
Thank you for your prompt reply and your comments!
On 05/28/2013 02:43 PM, Rafael J. Wysocki wrote:
>> With this patch the frequency can be increased to any value,
>
> What exactly does "any value" mean here?
>
I mean any value of freq table. Please let me know if you want me to rephrase
it in description.
> Can you please comment the results in the changelog? Attachments don't
> show up in git logs. :-)
I'm sorry, you are right. I added comments in the patch description.
>
> Can you please explain why this is the right formula?
>
Without this patch, we compare load_freq with up_threshold to decide about
the max frequency.
load_freq = load * freq_avg
In most cpufreq drivers getavg function is not implemented (I found that
it's implemented only in acpi-cpufreq). Therefore:
freq_avg = policy->cur.
Thus, in the comparison with up_threshold to increase frequency we actually
do this (in cases that getavg is not implemented):
if (load > up_theshold)
increase to max
So, after the patch we keep the same comparison to decide about the max frequency.
I thought, that below up_threshold is 'fair' to decide about the next
frequency with formula that frequency is proportional to load.
For example in a CPU with min freq 100MHz and max 1000MHz with a
load 50 target frequency should be 500MHz.
Thanks,
Stratos
-----------------------8<---------------------------------------------
Ondemand increases frequency only if the load_freq is greater than
up_threshold. This seems to produce oscillations of frequency between
min and max because a relatively small load can easily saturate minimum
frequency and lead the CPU to max. Then, the CPU will decrease back to
min due to a small load_freq.
With this patch the frequency can be increased to any value,
proportional to load, if the load is below up_threshold. Thus, middle
frequencies are used more. Absolute load is used for the calculation of
frequency.
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% to 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%
Signed-off-by: Stratos Karafotis <stratosk@...aphore.gr>
---
drivers/cpufreq/cpufreq_governor.c | 10 +---------
drivers/cpufreq/cpufreq_governor.h | 1 -
drivers/cpufreq/cpufreq_ondemand.c | 39 +++++++-------------------------------
3 files changed, 8 insertions(+), 42 deletions(-)
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 5af40ad..eeab30a 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -97,7 +97,7 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu)
policy = cdbs->cur_policy;
- /* Get Absolute Load (in terms of freq for ondemand gov) */
+ /* Get Absolute Load */
for_each_cpu(j, policy->cpus) {
struct cpu_dbs_common_info *j_cdbs;
u64 cur_wall_time, cur_idle_time;
@@ -148,14 +148,6 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu)
load = 100 * (wall_time - idle_time) / wall_time;
- if (dbs_data->cdata->governor == GOV_ONDEMAND) {
- int freq_avg = __cpufreq_driver_getavg(policy, j);
- if (freq_avg <= 0)
- freq_avg = policy->cur;
-
- load *= freq_avg;
- }
-
if (load > max_load)
max_load = load;
}
diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index e16a961..e899c11 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -169,7 +169,6 @@ struct od_dbs_tuners {
unsigned int sampling_rate;
unsigned int sampling_down_factor;
unsigned int up_threshold;
- unsigned int adj_up_threshold;
unsigned int powersave_bias;
unsigned int io_is_busy;
};
diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
index 4b9bb5d..c1e6d3e 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)
@@ -159,14 +157,10 @@ static void dbs_freq_increase(struct cpufreq_policy *p, unsigned int freq)
/*
* 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;
@@ -176,29 +170,17 @@ static void od_check_cpu(int cpu, unsigned int load_freq)
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->max / 100;
/* No longer fully busy, reset rate_mult */
dbs_info->rate_mult = 1;
@@ -372,9 +354,6 @@ static ssize_t store_up_threshold(struct dbs_data *dbs_data, const char *buf,
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;
@@ -523,8 +502,6 @@ static int od_init(struct dbs_data *dbs_data)
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
@@ -533,8 +510,6 @@ static int od_init(struct dbs_data *dbs_data)
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 *
--
1.8.1.4
--
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