[PATCH v2] cpufreq: conservative: Decrease frequency faster when the update deferred

From: Stratos Karafotis
Date: Sat Nov 12 2016 - 16:04:29 EST

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Conservative governor changes the CPU frequency in steps.
That means that if a CPU runs at max frequency, it will need several
sampling periods to return to min frequency when the workload
is finished.

If the update function that calculates the load and target frequency
is deferred, the governor might need even more time to decrease the
frequency.

This may have impact to power consumption and after all conservative
should decrease the frequency if there is no workload at every sampling
rate.

To resolve the above issue calculate the number of sampling periods
that the update is deferred. Considering that for each sampling period
conservative should drop the frequency by a freq_step because the
CPU was idle apply the proper subtraction to requested frequency.

Below, the kernel trace with and without this patch. First an
intensive workload is applied on a specific CPU. Then the workload
is removed and the CPU goes to idle.

WITHOUT

<idle>-0 [007] dN.. 620.329153: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 620.350857: cpu_frequency: state=1700000 cpu_id=7
kworker/7:2-556 [007] .... 620.370856: cpu_frequency: state=1900000 cpu_id=7
kworker/7:2-556 [007] .... 620.390854: cpu_frequency: state=2100000 cpu_id=7
kworker/7:2-556 [007] .... 620.411853: cpu_frequency: state=2200000 cpu_id=7
kworker/7:2-556 [007] .... 620.432854: cpu_frequency: state=2400000 cpu_id=7
kworker/7:2-556 [007] .... 620.453854: cpu_frequency: state=2600000 cpu_id=7
kworker/7:2-556 [007] .... 620.494856: cpu_frequency: state=2900000 cpu_id=7
kworker/7:2-556 [007] .... 620.515856: cpu_frequency: state=3100000 cpu_id=7
kworker/7:2-556 [007] .... 620.536858: cpu_frequency: state=3300000 cpu_id=7
kworker/7:2-556 [007] .... 620.557857: cpu_frequency: state=3401000 cpu_id=7
<idle>-0 [007] d... 669.591363: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 669.591939: cpu_idle: state=4294967295 cpu_id=7
<idle>-0 [007] d... 669.591980: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] dN.. 669.591989: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 670.201224: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 670.221975: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 670.222016: cpu_frequency: state=3300000 cpu_id=7
<idle>-0 [007] d... 670.222026: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 670.234964: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 670.801251: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 671.236046: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 671.236073: cpu_frequency: state=3100000 cpu_id=7
<idle>-0 [007] d... 671.236112: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 671.393437: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 671.401277: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 671.404083: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 671.404111: cpu_frequency: state=2900000 cpu_id=7
<idle>-0 [007] d... 671.404125: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 671.404974: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 671.501180: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 671.995414: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 671.995459: cpu_frequency: state=2800000 cpu_id=7
<idle>-0 [007] d... 671.995469: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 671.996287: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 672.001305: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.078374: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 672.078410: cpu_frequency: state=2600000 cpu_id=7
<idle>-0 [007] d... 672.078419: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.158020: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 672.158040: cpu_frequency: state=2400000 cpu_id=7
<idle>-0 [007] d... 672.158044: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.160038: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 672.234557: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.237121: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 672.237174: cpu_frequency: state=2100000 cpu_id=7
<idle>-0 [007] d... 672.237186: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.237778: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 672.267902: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.269860: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 672.269906: cpu_frequency: state=1900000 cpu_id=7
<idle>-0 [007] d... 672.269914: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.271902: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 672.751342: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 672.823056: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-556 [007] .... 672.823095: cpu_frequency: state=1600000 cpu_id=7

WITH

<idle>-0 [007] dN.. 4380.928009: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399 [007] .... 4380.949767: cpu_frequency: state=2000000 cpu_id=7
kworker/7:2-399 [007] .... 4380.969765: cpu_frequency: state=2200000 cpu_id=7
kworker/7:2-399 [007] .... 4381.009766: cpu_frequency: state=2500000 cpu_id=7
kworker/7:2-399 [007] .... 4381.029767: cpu_frequency: state=2600000 cpu_id=7
kworker/7:2-399 [007] .... 4381.049769: cpu_frequency: state=2800000 cpu_id=7
kworker/7:2-399 [007] .... 4381.069769: cpu_frequency: state=3000000 cpu_id=7
kworker/7:2-399 [007] .... 4381.089771: cpu_frequency: state=3100000 cpu_id=7
kworker/7:2-399 [007] .... 4381.109772: cpu_frequency: state=3400000 cpu_id=7
kworker/7:2-399 [007] .... 4381.129773: cpu_frequency: state=3401000 cpu_id=7
<idle>-0 [007] d... 4428.226159: cpu_idle: state=1 cpu_id=7
<idle>-0 [007] d... 4428.226176: cpu_idle: state=4294967295 cpu_id=7
<idle>-0 [007] d... 4428.226181: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 4428.227177: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 4428.551640: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 4428.649239: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399 [007] .... 4428.649268: cpu_frequency: state=2800000 cpu_id=7
<idle>-0 [007] d... 4428.649278: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 4428.689856: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 4428.799542: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 4428.801683: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399 [007] .... 4428.801748: cpu_frequency: state=1700000 cpu_id=7
<idle>-0 [007] d... 4428.801761: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 4428.806545: cpu_idle: state=4294967295 cpu_id=7
...
<idle>-0 [007] d... 4429.051880: cpu_idle: state=4 cpu_id=7
<idle>-0 [007] d... 4429.086240: cpu_idle: state=4294967295 cpu_id=7
kworker/7:2-399 [007] .... 4429.086293: cpu_frequency: state=1600000 cpu_id=7

Without the patch the CPU dropped to min frequency after 3.2s
With the patch applied the CPU dropped to min frequency after 0.86s

Signed-off-by: Stratos Karafotis <stratosk@xxxxxxxxxxxx>
---
v1 -> v2
- Use correct terminology in change log
- Change the member variable name from 'deferred_periods' to 'idle_periods'
- Fix format issue

drivers/cpufreq/cpufreq_conservative.c | 14 +++++++++++++-
drivers/cpufreq/cpufreq_governor.c | 18 +++++++++++++-----
drivers/cpufreq/cpufreq_governor.h | 1 +
3 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c
index fa5ece3..d787772 100644
--- a/drivers/cpufreq/cpufreq_conservative.c
+++ b/drivers/cpufreq/cpufreq_conservative.c
@@ -73,7 +73,19 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy)
*/
if (cs_tuners->freq_step == 0)
goto out;
-
+ /*
+ * Decrease requested_freq for each idle period that we didn't
+ * update the frequency
+ */
+ if (policy_dbs->idle_periods < UINT_MAX) {
+ unsigned int freq_target = policy_dbs->idle_periods *
+ get_freq_target(cs_tuners, policy);
+ if (requested_freq > freq_target)
+ requested_freq -= freq_target;
+ else
+ requested_freq = policy->min;
+ policy_dbs->idle_periods = UINT_MAX;
+ }
/*
* If requested_freq is out of range, it is likely that the limits
* changed in the meantime, so fall back to current frequency in that
diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
index 3729474..1bc7137 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -117,7 +117,7 @@ unsigned int dbs_update(struct cpufreq_policy *policy)
struct policy_dbs_info *policy_dbs = policy->governor_data;
struct dbs_data *dbs_data = policy_dbs->dbs_data;
unsigned int ignore_nice = dbs_data->ignore_nice_load;
- unsigned int max_load = 0;
+ unsigned int max_load = 0, idle_periods = UINT_MAX;
unsigned int sampling_rate, io_busy, j;

/*
@@ -163,8 +163,12 @@ unsigned int dbs_update(struct cpufreq_policy *policy)
* calls, so the previous load value can be used then.
*/
load = j_cdbs->prev_load;
- } else if (unlikely(time_elapsed > 2 * sampling_rate &&
- j_cdbs->prev_load)) {
+ } else if (unlikely(time_elapsed > 2 * sampling_rate)) {
+ unsigned int periods = time_elapsed / sampling_rate;
+
+ if (periods < idle_periods)
+ idle_periods = periods;
+
/*
* If the CPU had gone completely idle and a task has
* just woken up on this CPU now, it would be unfair to
@@ -189,8 +193,10 @@ unsigned int dbs_update(struct cpufreq_policy *policy)
* 'time_elapsed' (as compared to the sampling rate)
* indicates this scenario.
*/
- load = j_cdbs->prev_load;
- j_cdbs->prev_load = 0;
+ if (j_cdbs->prev_load) {
+ load = j_cdbs->prev_load;
+ j_cdbs->prev_load = 0;
+ }
} else {
if (time_elapsed >= idle_time) {
load = 100 * (time_elapsed - idle_time) / time_elapsed;
@@ -218,6 +224,8 @@ unsigned int dbs_update(struct cpufreq_policy *policy)
if (load > max_load)
max_load = load;
}
+ policy_dbs->idle_periods = idle_periods;
+
return max_load;
}
EXPORT_SYMBOL_GPL(dbs_update);
diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h
index 9660cc6..10a3e0a 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -97,6 +97,7 @@ struct policy_dbs_info {
struct list_head list;
/* Multiplier for increasing sample delay temporarily. */
unsigned int rate_mult;
+ unsigned int idle_periods;
/* Status indicators */
bool is_shared; /* This object is used by multiple CPUs */
bool work_in_progress; /* Work is being queued up or in progress */
--
2.7.4

Next message: Matt Fleming: "[GIT PULL 0/2] EFI urgent fixes"
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Next in thread: Viresh Kumar: "Re: [PATCH v2] cpufreq: conservative: Decrease frequency faster when the update deferred"
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