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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2023-08-03 23:11:40 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2023-08-09 19:58:53 +0200
commit2662342079f54b8a940f7094c197c99458caeb0d (patch)
treed5142e37398951a734c6edec349d9292326ae2eb /drivers/cpuidle
parent6da8f9ba5a87f8aecf2cd4441cc6024a77e5b645 (diff)
cpuidle: teo: Gather statistics regarding whether or not to stop the tick
Currently, if the target residency of the deepest idle state is less than the tick period length, which is quite likely for HZ=100, and the deepest idle state is about to be selected by the TEO idle governor, the decision on whether or not to stop the scheduler tick is based entirely on the time till the closest timer. This is often insufficient, because timers may not be in heavy use and there may be a plenty of other CPU wakeup events between the deepest idle state's target residency and the closest tick. Allow the governor to count those events by making the deepest idle state's bin effectively end at TICK_NSEC and introducing an additional "bin" for collecting "hit" events (ie. the ones in which the measured idle duration falls into the same bin as the time till the closest timer) with idle duration values past TICK_NSEC. This way the "intercepts" metric for the deepest idle state's bin becomes nonzero in general, and so it can influence the decision on whether or not to stop the tick possibly increasing the governor's accuracy in that respect. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com> Tested-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Diffstat (limited to 'drivers/cpuidle')
-rw-r--r--drivers/cpuidle/governors/teo.c41
1 files changed, 40 insertions, 1 deletions
diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
index 8248492cad3a..70846b669255 100644
--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -192,6 +192,7 @@ struct teo_bin {
* @total: Grand total of the "intercepts" and "hits" metrics for all bins.
* @next_recent_idx: Index of the next @recent_idx entry to update.
* @recent_idx: Indices of bins corresponding to recent "intercepts".
+ * @tick_hits: Number of "hits" after TICK_NSEC.
* @util_threshold: Threshold above which the CPU is considered utilized
*/
struct teo_cpu {
@@ -201,6 +202,7 @@ struct teo_cpu {
unsigned int total;
int next_recent_idx;
int recent_idx[NR_RECENT];
+ unsigned int tick_hits;
unsigned long util_threshold;
};
@@ -232,6 +234,7 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
{
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
int i, idx_timer = 0, idx_duration = 0;
+ s64 target_residency_ns;
u64 measured_ns;
if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) {
@@ -272,7 +275,6 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
* fall into.
*/
for (i = 0; i < drv->state_count; i++) {
- s64 target_residency_ns = drv->states[i].target_residency_ns;
struct teo_bin *bin = &cpu_data->state_bins[i];
bin->hits -= bin->hits >> DECAY_SHIFT;
@@ -280,6 +282,8 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
cpu_data->total += bin->hits + bin->intercepts;
+ target_residency_ns = drv->states[i].target_residency_ns;
+
if (target_residency_ns <= cpu_data->sleep_length_ns) {
idx_timer = i;
if (target_residency_ns <= measured_ns)
@@ -295,6 +299,26 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
cpu_data->state_bins[cpu_data->recent_idx[i]].recent--;
/*
+ * If the deepest state's target residency is below the tick length,
+ * make a record of it to help teo_select() decide whether or not
+ * to stop the tick. This effectively adds an extra hits-only bin
+ * beyond the last state-related one.
+ */
+ if (target_residency_ns < TICK_NSEC) {
+ cpu_data->tick_hits -= cpu_data->tick_hits >> DECAY_SHIFT;
+
+ cpu_data->total += cpu_data->tick_hits;
+
+ if (TICK_NSEC <= cpu_data->sleep_length_ns) {
+ idx_timer = drv->state_count;
+ if (TICK_NSEC <= measured_ns) {
+ cpu_data->tick_hits += PULSE;
+ goto end;
+ }
+ }
+ }
+
+ /*
* If the measured idle duration falls into the same bin as the sleep
* length, this is a "hit", so update the "hits" metric for that bin.
* Otherwise, update the "intercepts" metric for the bin fallen into by
@@ -309,6 +333,7 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
cpu_data->recent_idx[i] = idx_duration;
}
+end:
cpu_data->total += PULSE;
}
@@ -356,6 +381,7 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
s64 latency_req = cpuidle_governor_latency_req(dev->cpu);
ktime_t delta_tick = TICK_NSEC / 2;
+ unsigned int tick_intercept_sum = 0;
unsigned int idx_intercept_sum = 0;
unsigned int intercept_sum = 0;
unsigned int idx_recent_sum = 0;
@@ -429,6 +455,8 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
hit_sum += prev_bin->hits;
recent_sum += prev_bin->recent;
+ tick_intercept_sum = intercept_sum;
+
if (dev->states_usage[i].disable)
continue;
@@ -461,6 +489,8 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
goto end;
}
+ tick_intercept_sum += cpu_data->state_bins[drv->state_count-1].intercepts;
+
/*
* If the sum of the intercepts metric for all of the idle states
* shallower than the current candidate one (idx) is greater than the
@@ -577,6 +607,15 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
idx = i;
}
+ /*
+ * If the selected state's target residency is below the tick length
+ * and intercepts occurring before the tick length are the majority of
+ * total wakeup events, do not stop the tick.
+ */
+ if (drv->states[idx].target_residency_ns < TICK_NSEC &&
+ tick_intercept_sum > cpu_data->total / 2 + cpu_data->total / 8)
+ duration_ns = TICK_NSEC / 2;
+
end:
/*
* Allow the tick to be stopped unless the selected state is a polling