On Wed, 25 Jan 2023 at 17:46, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx> wrote: > > > Hi Krzysztof, > > > On 25/01/2023 12:34, 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 idle callbacks in cpuidle-psci and mark the domain as > > always on. This is a trade-off between making PREEMPT_RT working and > > still having a proper power domain hierarchy in the system. > > Wouldn't make sense to rely on the latency constraint framework ? The main problem is that for runtime PM there is a per device spinlock being used, which becomes a sleepable lock on PREEMPT_RT. In other words, the only simple solution is to avoid the calls to runtime PM in the idle path. [...] Kind regards Uffe
