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cpuidle: governors: teo: Decay metrics below DECAY_SHIFT threshold

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If a given governor metric falls below a certain value (8 for
DECAY_SHIFT equal to 3), it will not decay any more due to the
simplistic decay implementation.  This may in some cases lead to
subtle inconsistencies in the governor behavior, so change the
decay implementation to take it into account and set the metric
at hand to 0 in that case.

Suggested-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Tested-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/2819353.mvXUDI8C0e@rafael.j.wysocki
This commit is contained in:
Rafael J. Wysocki
2025-11-12 19:03:08 +01:00
parent 8f3f01082d
commit b54df61c74
1 changed files with 19 additions and 7 deletions
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26
drivers/cpuidle/governors/teo.c
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@@ -148,6 +148,16 @@ struct teo_cpu {
static DEFINE_PER_CPU(struct teo_cpu, teo_cpus);
static void teo_decay(unsigned int *metric)
{
unsigned int delta = *metric >> DECAY_SHIFT;
if (delta)
*metric -= delta;
else
*metric = 0;
}
/**
* teo_update - Update CPU metrics after wakeup.
* @drv: cpuidle driver containing state data.
@@ -158,8 +168,9 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
struct teo_cpu *cpu_data = this_cpu_ptr(&teo_cpus);
int i, idx_timer = 0, idx_duration = 0;
s64 target_residency_ns, measured_ns;
unsigned int total = 0;
cpu_data->short_idles -= cpu_data->short_idles >> DECAY_SHIFT;
teo_decay(&cpu_data->short_idles);
if (cpu_data->artificial_wakeup) {
/*
@@ -195,8 +206,10 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
for (i = 0; i < drv->state_count; i++) {
struct teo_bin *bin = &cpu_data->state_bins[i];
bin->hits -= bin->hits >> DECAY_SHIFT;
bin->intercepts -= bin->intercepts >> DECAY_SHIFT;
teo_decay(&bin->hits);
total += bin->hits;
teo_decay(&bin->intercepts);
total += bin->intercepts;
target_residency_ns = drv->states[i].target_residency_ns;
@@ -207,7 +220,9 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
}
}
cpu_data->tick_intercepts -= cpu_data->tick_intercepts >> DECAY_SHIFT;
cpu_data->total = total + PULSE;
teo_decay(&cpu_data->tick_intercepts);
/*
* 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.
@@ -221,9 +236,6 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
if (TICK_NSEC <= measured_ns)
cpu_data->tick_intercepts += PULSE;
}
cpu_data->total -= cpu_data->total >> DECAY_SHIFT;
cpu_data->total += PULSE;
}
static bool teo_state_ok(int i, struct cpuidle_driver *drv)