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Re: [RFC v0 2/9] suspend: Add getter function to report if freezing is active

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On 09/05/2015 04:11 AM, Rafael J. Wysocki wrote:
> On Friday, September 04, 2015 03:34:55 PM Daniel Wagner wrote:
>> Instead encode the FREEZE state via the CPU state we allow the
>> interesting subsystems (MCE, microcode) to query the power
>> subsystem directly.
> 
> A use case, please.

The motivation for this change is to reduce the complexity in the
hotplug code. As tried to point out in the cover letter, the FROZEN
bits have only a bunch of users after all those years (2007). So it is
worth to have all the notifier users to handle the FROZEN state?

Don't know if that counts as use case.

>> Most notifiers are not interested at all
>> in this information so rather have explicit calls to freeze_active()
>> instead adding complexity to the rest of the users of the CPU
>> notifiers.
> 
> Why does it has anything to do with CPU notifiers?

cpu_{down|up} will call the notifiers with the CPU_TASK_FROZEN bit set
and so most notifiers are doing

	switch (actcion ~CPU_TASK_FROZEN)

to filter it out because they don't need to handle the system wide
ongoing freeze operations.

> We don't offline CPUs for suspend-to-idle.

Sure. As I said the motivation is to reduce the complexity in the
hotplug code.

Thanks,
Daniel
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Thread

[RFC v0 0/9] Remove CPU_*_FROZEN Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 8/9] cpu: Do not set CPU_TASKS_FROZEN anymore Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 1/9] smpboot: Add a separate CPU state when a surviving CPU times out Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 2/9] suspend: Add getter function to report if freezing is active Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
    Re: [RFC v0 2/9] suspend: Add getter function to report if freezing is active "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-05 03:50 +0200
      Re: [RFC v0 2/9] suspend: Add getter function to report if freezing  is active Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-07 11:00 +0200
        Re: [RFC v0 2/9] suspend: Add getter function to report if freezing is active "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-07 15:20 +0200
        Re: [RFC v0 2/9] suspend: Add getter function to report if freezing is active "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2015-09-07 23:20 +0200
          Re: [RFC v0 2/9] suspend: Add getter function to report if freezing  is active Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-08 10:20 +0200
  [RFC v0 5/9] sched: Use freeze_active() instead CPU_*_FROZEN state information Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 4/9] smpboot: Use freeze_active() instead CPU_DEAD_FROZEN state information Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
    Re: [RFC v0 4/9] smpboot: Use freeze_active() instead CPU_DEAD_FROZEN  state information Daniel Wagner <wagi@monom.org> - 2015-09-08 10:50 +0200
  [RFC v0 6/9] cpu: Restructure FROZEN state handling Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 3/9] x86: Use freeze_active() instead of CPU_*_FROZEN Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200
  [RFC v0 9/9] doc: Update cpu-hotplug documents on removal of CPU_TASKS_FROZEN Daniel Wagner <daniel.wagner@bmw-carit.de> - 2015-09-04 15:40 +0200

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