Messages in this thread | | | Date | Wed, 25 Jan 2023 08:42:59 +0100 | Subject | Re: [PATCH v3] cpuidle: psci: Do not suspend topology CPUs on PREEMPT_RT | From | Krzysztof Kozlowski <> |
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On 24/01/2023 16:34, Sudeep Holla wrote: > 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@redhat.com> >> Cc: Brian Masney <bmasney@redhat.com> >> Cc: linux-rt-users@vger.kernel.org >> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org> >> >> --- >> >> 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 ?
It's the power domain sued for other devices, so we need it. Otherwise other devices will keep waiting for this missing power domain provider.
Best regards, Krzysztof
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