Commit db86f55b authored by Rafael J. Wysocki's avatar Rafael J. Wysocki
Browse files

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

A throughput regression of 11% introduced by commit 779b1a1c ("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: 779b1a1c ("cpuidle: governors: menu: Avoid selecting states with too much latency")
Closes: https://lore.kernel.org/linux-pm/004501dc43c9$ec8aa930$c59ffb90$@telus.net/


Reported-by: default avatarDoug Smythies <dsmythies@telus.net>
Tested-by: default avatarDoug Smythies <dsmythies@telus.net>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: default avatarChristian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/12786727.O9o76ZdvQC@rafael.j.wysocki
parent dcb6fa37

drivers/cpuidle/governors/menu.c

+5 −2
Original line number Diff line number Diff line
@@ -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;