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

A throughput regression of 11% introduced by commit 779b1a1 ("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: 779b1a1 ("cpuidle: governors: menu: Avoid selecting states with too much latency")
Closes: https://lore.kernel.org/linux-pm/[email protected]/
Reported-by: Doug Smythies <[email protected]>
Tested-by: Doug Smythies <[email protected]>
Cc: All applicable <[email protected]>
Signed-off-by: Rafael J. Wysocki <[email protected]>
Reviewed-by: Christian Loehle <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: rafaeljw

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;