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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2023-07-31 20:56:35 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2023-08-03 22:36:09 +0200
commit3f0b0966b30982e843950b170b7a9ddfd8094428 (patch)
treec7749ffb176628a1208075dd7bf372c2f7fa8b66 /drivers/cpuidle
parent5d0c230f1de8c7515b6567d9afba1f196fb4e2f4 (diff)
downloadlwn-3f0b0966b30982e843950b170b7a9ddfd8094428.tar.gz
lwn-3f0b0966b30982e843950b170b7a9ddfd8094428.zip
cpuidle: teo: Update idle duration estimate when choosing shallower state
The TEO governor takes CPU utilization into account by refining idle state selection when the utilization is above a certain threshold. This is done by choosing an idle state shallower than the previously selected one. However, when doing this, the idle duration estimate needs to be adjusted so as to prevent the scheduler tick from being stopped when the candidate idle state is shallow, which may lead to excessive energy usage if the CPU is not woken up quickly enough going forward. Moreover, if the scheduler tick has been stopped already and the new idle duration estimate is too small, the replacement candidate state cannot be used. Modify the relevant code to take the above observations into account. Fixes: 9ce0f7c4bc64 ("cpuidle: teo: Introduce util-awareness") Link: https://lore.kernel.org/linux-pm/CAJZ5v0jJxHj65r2HXBTd3wfbZtsg=_StzwO1kA5STDnaPe_dWA@mail.gmail.com Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Reviewed-and-tested-by: Kajetan Puchalski <kajetan.puchalski@arm.com>
Diffstat (limited to 'drivers/cpuidle')
-rw-r--r--drivers/cpuidle/governors/teo.c40
1 files changed, 30 insertions, 10 deletions
diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
index 987fc5f3997d..2cdc711679a5 100644
--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -397,13 +397,23 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
* the shallowest non-polling state and exit.
*/
if (drv->state_count < 3 && cpu_data->utilized) {
- for (i = 0; i < drv->state_count; ++i) {
- if (!dev->states_usage[i].disable &&
- !(drv->states[i].flags & CPUIDLE_FLAG_POLLING)) {
- idx = i;
- goto end;
- }
- }
+ /* The CPU is utilized, so assume a short idle duration. */
+ duration_ns = teo_middle_of_bin(0, drv);
+ /*
+ * If state 0 is enabled and it is not a polling one, select it
+ * right away unless the scheduler tick has been stopped, in
+ * which case care needs to be taken to leave the CPU in a deep
+ * enough state in case it is not woken up any time soon after
+ * all. If state 1 is disabled, though, state 0 must be used
+ * anyway.
+ */
+ if ((!idx && !(drv->states[0].flags & CPUIDLE_FLAG_POLLING) &&
+ teo_time_ok(duration_ns)) || dev->states_usage[1].disable)
+ idx = 0;
+ else /* Assume that state 1 is not a polling one and use it. */
+ idx = 1;
+
+ goto end;
}
/*
@@ -539,10 +549,20 @@ static int teo_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
/*
* If the CPU is being utilized over the threshold, choose a shallower
- * non-polling state to improve latency
+ * non-polling state to improve latency, unless the scheduler tick has
+ * been stopped already and the shallower state's target residency is
+ * not sufficiently large.
*/
- if (cpu_data->utilized)
- idx = teo_find_shallower_state(drv, dev, idx, duration_ns, true);
+ if (cpu_data->utilized) {
+ s64 span_ns;
+
+ i = teo_find_shallower_state(drv, dev, idx, duration_ns, true);
+ span_ns = teo_middle_of_bin(i, drv);
+ if (teo_time_ok(span_ns)) {
+ idx = i;
+ duration_ns = span_ns;
+ }
+ }
end:
/*