6.17-stable review patch. If anyone has any objections, please let me know.
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From: "Rafael J. Wysocki" rafael.j.wysocki@intel.com
[ Upstream commit db86f55bf81a3a297be05ee8775ae9a8c6e3a599 ]
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%24ec8aa930%24c59ffb90%24@telus... 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 Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/cpuidle/governors/menu.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)
--- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -318,10 +318,13 @@ static int menu_select(struct cpuidle_dr
/* * 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;