On Thu, 21 Oct 2021 at 15:45, Rafael J. Wysocki [off-list ref] wrote:

On Thu, Oct 21, 2021 at 1:49 PM Ulf Hansson [off-list ref] wrote:

quoted

On Wed, 20 Oct 2021 at 20:18, Rafael J. Wysocki [off-list ref] wrote:

quoted

On Wed, Sep 29, 2021 at 4:44 PM Ulf Hansson [off-list ref] wrote:

quoted

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 [off-list ref]
Suggested-by: Maulik Shah <redacted>
Signed-off-by: Ulf Hansson <redacted>
---
 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.

quoted

quoted

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.

quoted

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.

The use case I want to support, for cpuidle-psci, is to allow all idle
states in suspend-to-idle, but prevent those that rely on runtime PM
(after it has been disabled) for the regular idle path.

quoted

Is this really what we want?

quoted

The other guys who rely on the cpuidle pausing today could be switched
over to this new mechanism later and it would be possible to get rid
of the pausing from the system suspend path completely.

Avoiding to pause cpuidle when it's not needed makes perfect sense.
Although, it looks to me that we could also implement that on top of
$subject patch.

Yes, it could.

quoted

Unless you insist on the CPUIDLE_STATE_DISABLED_ way, I would probably
explore an option to let a cpuidle driver to set a global cpuidle flag
during ->probe(). Depending if this flag is set, we can simply skip
calling cpuidle_pause() during system suspend.

What do you think?

Well, which driver in particular is in question here?

Honestly, I don't know. It has not been my goal to entirely prevent
calling cpuidle_pause().

In any case, it was introduced in the below commit, perhaps that can
give us a hint when this is still needed?

commit 8651f97bd951d0bb1c10fa24e3fa3455193f3548
Author: Preeti U Murthy [off-list ref]
Date:   Mon Jul 9 10:12:56 2012 +0200
PM / cpuidle: System resume hang fix with cpuidle

Kind regards
Uffe