On Thu, Jan 19, 2023 at 07:42:28PM +0100, Krzysztof Kozlowski wrote: > The runtime Power Management of CPU topology is not compatible with > PREEMPT_RT: > 1. Core cpuidle path disables IRQs. > 2. Core cpuidle calls cpuidle-psci. > 3. cpuidle-psci in __psci_enter_domain_idle_state() calls > pm_runtime_put_sync_suspend() and pm_runtime_get_sync() which use > spinlocks (which are sleeping on PREEMPT_RT). > > Deep sleep modes are not a priority of Realtime kernels because the > latencies might become unpredictable. On the other hand the PSCI CPU > idle power domain is a parent of other devices and power domain > controllers, thus it cannot be simply skipped (e.g. on Qualcomm SM8250). > > Disable the runtime PM calls from cpuidle-psci, which effectively stops > suspending the cpuidle PSCI domain. This is a trade-off between making > PREEMPT_RT working and still having a proper power domain hierarchy in > the system. > > Cc: Adrien Thierry <athierry@xxxxxxxxxx> > Cc: Brian Masney <bmasney@xxxxxxxxxx> > Cc: linux-rt-users@xxxxxxxxxxxxxxx > Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> > > --- > > Changes since v1: > 1. Re-work commit msg. > 2. Add note to Kconfig. > > Several other patches were dropped, as this is the only one actually > needed. It effectively stops PSCI cpuidle power domains from suspending > thus solving all other issues I experienced. > --- > drivers/cpuidle/Kconfig.arm | 3 +++ > drivers/cpuidle/cpuidle-psci.c | 4 ++-- > 2 files changed, 5 insertions(+), 2 deletions(-) > > diff --git a/drivers/cpuidle/Kconfig.arm b/drivers/cpuidle/Kconfig.arm > index 747aa537389b..24429b5bfd1c 100644 > --- a/drivers/cpuidle/Kconfig.arm > +++ b/drivers/cpuidle/Kconfig.arm > @@ -24,6 +24,9 @@ config ARM_PSCI_CPUIDLE > It provides an idle driver that is capable of detecting and > managing idle states through the PSCI firmware interface. > > + The driver is not yet compatible with PREEMPT_RT: no idle states will > + be entered by CPUs on such kernel. > + Any particular reason for even compiling this file in or allowing the ARM_PSCI_CPUIDLE when PREEMPT_RT=y ? If we can't enter idle states, we can as well compile this file out ? -- Regards, Sudeep
