From 32b91ca15353b2803d27cfc747156e72dd2cd5d8 Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Thu, 18 Jul 2019 10:53:21 +0200 Subject: cpuidle: menu: Allow tick to be stopped if PM QoS is used After commit 554c8aa8ecad ("sched: idle: Select idle state before stopping the tick") the menu governor prevents the scheduler tick from being stopped (unless stopped already) if there is a PM QoS latency constraint for the given CPU and the target residency of the deepest idle state matching that constraint is below the tick boundary. However, that is problematic if CPUs with PM QoS latency constraints are idle for long times, because it effectively causes the tick to run on them all the time which is wasteful. [It is also confusing and questionable if they are full dynticks CPUs.] To address that issue, make the menu governor allow the tick to be stopped only if the idle duration predicted by it is beyond the tick boundary, except when the shallowest idle state is selected upfront and it is not a "polling" one. Fixes: 554c8aa8ecad ("sched: idle: Select idle state before stopping the tick") Link: https://lore.kernel.org/lkml/79b247b3-e056-610e-9a07-e685dfdaa6c9@gmail.com/ Reported-by: Thomas Lindroth Tested-by: Thomas Lindroth Signed-off-by: Rafael J. Wysocki --- drivers/cpuidle/governors/menu.c | 16 +++++----------- 1 file changed, 5 insertions(+), 11 deletions(-) diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c index dace4c7f830c..e5a5d0c8d66b 100644 --- a/drivers/cpuidle/governors/menu.c +++ b/drivers/cpuidle/governors/menu.c @@ -301,9 +301,10 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, !drv->states[0].disabled && !dev->states_usage[0].disable)) { /* * In this case state[0] will be used no matter what, so return - * it right away and keep the tick running. + * it right away and keep the tick running if state[0] is a + * polling one. */ - *stop_tick = false; + *stop_tick = !(drv->states[0].flags & CPUIDLE_FLAG_POLLING); return 0; } @@ -394,16 +395,9 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev, return idx; } - if (s->exit_latency > latency_req) { - /* - * If we break out of the loop for latency reasons, use - * the target residency of the selected state as the - * expected idle duration so that the tick is retained - * as long as that target residency is low enough. - */ - predicted_us = drv->states[idx].target_residency; + if (s->exit_latency > latency_req) break; - } + idx = i; } -- cgit v1.2.3