On 12/01/2023 12:09, Sebastian Andrzej Siewior wrote: > On 2022-12-19 16:15:01 [+0100], Krzysztof Kozlowski wrote: >> diff --git a/drivers/cpuidle/cpuidle-psci.c b/drivers/cpuidle/cpuidle-psci.c >> index 57bc3e3ae391..9d971cc4b12b 100644 >> --- a/drivers/cpuidle/cpuidle-psci.c >> +++ b/drivers/cpuidle/cpuidle-psci.c >> @@ -72,7 +72,7 @@ static int __psci_enter_domain_idle_state(struct cpuidle_device *dev, >> ct_irq_enter_irqson(); >> if (s2idle) >> dev_pm_genpd_suspend(pd_dev); >> - else >> + else if (!IS_ENABLED(CONFIG_PREEMPT_RT)) >> pm_runtime_put_sync_suspend(pd_dev); > > So based on the commit description you run into a sleeping lock in > pm_runtime_put_sync_suspend() while the CPU is in an IRQ-off region. > Why is it okay to skip it on PREEMPT_RT? It is okay to skip it everywhere, you just don't get a suspended CPU. Why PREEMPT_RT is different here - having suspended CPU is a great way to have longer or even unpredictable (as it goes to firmware which is out of control of Linux) latencies. Best regards, Krzysztof
