cpuidle: governors: menu: Select polling state in some more cases

A throughput regression of 11% introduced by commit 779b1a1cb13a ("cpuidle:
governors: menu: Avoid selecting states with too much latency") has been
reported and it is related to the case when the menu governor checks if
selecting a proper idle state instead of a polling one makes sense.

In particular, it is questionable to do so if the exit latency of the
idle state in question exceeds the predicted idle duration, so add a
check for that, which is sufficient to make the reported regression go
away, and update the related code comment accordingly.

Fixes: 779b1a1cb13a ("cpuidle: governors: menu: Avoid selecting states with too much latency")
Closes: https://lore.kernel.org/linux-pm/004501dc43c9$ec8aa930$c59ffb90$@telus.net/
Reported-by: Doug Smythies <dsmythies@telus.net>
Tested-by: Doug Smythies <dsmythies@telus.net>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/12786727.O9o76ZdvQC@rafael.j.wysocki

diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index 7d21fb5a72f40ceaeb10cfbae3ded242a87dc555..23239b0c04f95b05845e97c97116800fe0c89125 100644 (file)
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -318,10 +318,13 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
 
                /*
                 * Use a physical idle state, not busy polling, unless a timer
-                * is going to trigger soon enough.
+                * is going to trigger soon enough or the exit latency of the
+                * idle state in question is greater than the predicted idle
+                * duration.
                 */
                if ((drv->states[idx].flags & CPUIDLE_FLAG_POLLING) &&
-                   s->target_residency_ns <= data->next_timer_ns) {
+                   s->target_residency_ns <= data->next_timer_ns &&
+                   s->exit_latency_ns <= predicted_ns) {
                        predicted_ns = s->target_residency_ns;
                        idx = i;
                        break;