Messages in this thread | | | From | "Rafael J. Wysocki" <> | Date | Thu, 21 Oct 2021 18:33:19 +0200 | Subject | Re: [PATCH 2/2] PM: sleep: Fix runtime PM based cpuidle support |
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On Thu, Oct 21, 2021 at 6:17 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > On Thu, 21 Oct 2021 at 17:09, Rafael J. Wysocki <rafael@kernel.org> wrote: > > > > On Thu, Oct 21, 2021 at 4:05 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > On Thu, 21 Oct 2021 at 15:45, Rafael J. Wysocki <rafael@kernel.org> wrote: > > > > > > > > On Thu, Oct 21, 2021 at 1:49 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > > > > > On Wed, 20 Oct 2021 at 20:18, Rafael J. Wysocki <rafael@kernel.org> wrote: > > > > > > > > > > > > On Wed, Sep 29, 2021 at 4:44 PM Ulf Hansson <ulf.hansson@linaro.org> wrote: > > > > > > > > > > > > > > In the cpuidle-psci case, runtime PM in combination with the generic PM > > > > > > > domain (genpd), may be used when entering/exiting an idlestate. More > > > > > > > precisely, genpd relies on runtime PM to be enabled for the attached device > > > > > > > (in this case it belongs to a CPU), to properly manage the reference > > > > > > > counting of its PM domain. > > > > > > > > > > > > > > This works fine most of the time, but during system suspend in the > > > > > > > dpm_suspend_late() phase, the PM core disables runtime PM for all devices. > > > > > > > Beyond this point and until runtime PM becomes re-enabled in the > > > > > > > dpm_resume_early() phase, calls to pm_runtime_get|put*() will fail. > > > > > > > > > > > > > > To make sure the reference counting in genpd becomes correct, we need to > > > > > > > prevent cpuidle-psci from using runtime PM when it has been disabled for > > > > > > > the device. Therefore, let's move the call to cpuidle_pause() from > > > > > > > dpm_suspend_noirq() to dpm_suspend_late() - and cpuidle_resume() from > > > > > > > dpm_resume_noirq() into dpm_resume_early(). > > > > > > > > > > > > > > Diagnosed-by: Maulik Shah <mkshah@codeaurora.org> > > > > > > > Suggested-by: Maulik Shah <mkshah@codeaurora.org> > > > > > > > Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org> > > > > > > > --- > > > > > > > drivers/base/power/main.c | 6 ++---- > > > > > > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > > > > > > > > > > > diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c > > > > > > > index cbea78e79f3d..1c753b651272 100644 > > > > > > > --- a/drivers/base/power/main.c > > > > > > > +++ b/drivers/base/power/main.c > > > > > > > @@ -747,8 +747,6 @@ void dpm_resume_noirq(pm_message_t state) > > > > > > > > > > > > > > resume_device_irqs(); > > > > > > > device_wakeup_disarm_wake_irqs(); > > > > > > > - > > > > > > > - cpuidle_resume(); > > > > > > > } > > > > > > > > > > > > > > /** > > > > > > > @@ -870,6 +868,7 @@ void dpm_resume_early(pm_message_t state) > > > > > > > } > > > > > > > mutex_unlock(&dpm_list_mtx); > > > > > > > async_synchronize_full(); > > > > > > > + cpuidle_resume(); > > > > > > > dpm_show_time(starttime, state, 0, "early"); > > > > > > > trace_suspend_resume(TPS("dpm_resume_early"), state.event, false); > > > > > > > } > > > > > > > @@ -1336,8 +1335,6 @@ int dpm_suspend_noirq(pm_message_t state) > > > > > > > { > > > > > > > int ret; > > > > > > > > > > > > > > - cpuidle_pause(); > > > > > > > - > > > > > > > device_wakeup_arm_wake_irqs(); > > > > > > > suspend_device_irqs(); > > > > > > > > > > > > > > @@ -1467,6 +1464,7 @@ int dpm_suspend_late(pm_message_t state) > > > > > > > int error = 0; > > > > > > > > > > > > > > trace_suspend_resume(TPS("dpm_suspend_late"), state.event, true); > > > > > > > + cpuidle_pause(); > > > > > > > mutex_lock(&dpm_list_mtx); > > > > > > > pm_transition = state; > > > > > > > async_error = 0; > > > > > > > -- > > > > > > > > > > > > Well, this is somewhat heavy-handed and it affects even the systems > > > > > > that don't really need to pause cpuidle at all in the suspend path. > > > > > > > > > > Yes, I agree. > > > > > > > > > > Although, I am not really changing the behaviour in regards to this. > > > > > cpuidle_pause() is already being called in dpm_suspend_noirq(), for > > > > > everybody today. > > > > > > > > Yes, it is, but pausing it earlier will cause more energy to be spent, > > > > potentially. > > > > > > > > That said, there are not too many users of suspend_late callbacks in > > > > the tree, so it may not matter too much. > > > > > > > > > > > > > > > > Also, IIUC you don't need to pause cpuidle completely, but make it > > > > > > temporarily avoid idle states potentially affected by this issue. An > > > > > > additional CPUIDLE_STATE_DISABLED_ flag could be used for that I > > > > > > suppose and it could be set via cpuidle_suspend() called from the core > > > > > > next to cpufreq_suspend(). > > > > > > > > > > cpuidle_suspend() would then need to go and fetch the cpuidle driver > > > > > instance, which in some cases is one driver per CPU. Doesn't that get > > > > > rather messy? > > > > > > > > Per-CPU variables are used for that, so it is quite straightforward. > > > > > > > > > Additionally, since find_deepest_state() is being called for > > > > > cpuidle_enter_s2idle() too, we would need to treat the new > > > > > CPUIDLE_STATE_DISABLED_ flag in a special way, right? > > > > > > > > No, it already checks "disabled". > > > > > > Yes, but that would be wrong. > > > > Hmmm. > > > > > The use case I want to support, for cpuidle-psci, is to allow all idle > > > states in suspend-to-idle, > > > > So does PM-runtime work in suspend-to-idle? How? > > No it doesn't. See below. > > > > > > but prevent those that rely on runtime PM > > > (after it has been disabled) for the regular idle path. > > > > Do you have a special suspend-to-idle handling of those states that > > doesn't require PM-runtime? > > Yes. Feel free to have a look in __psci_enter_domain_idle_state().
So in theory you could check the pm_runtime_put_sync_suspend() return value and fall back to something like WFI if that's an error code.
> In principle, when running the s2idle path, we call > dev_pm_genpd_suspend|resume(), rather than pm_runtime_get|put*. > > This let genpd manage the reference counting (hierarchically too) and > it also ignores the genpd governor in this stage, which also is needed > to enter the deepest state. Quite similar to how cpuidle works.
OK
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