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Re: [PATCH v4 22/22] thermal/intel_powerclamp: Convert the kthread to kthread worker API

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On Mon, 25 Jan 2016 16:45:11 +0100
Petr Mladek <pmladek@suse.com> wrote:

> Kthreads are currently implemented as an infinite loop. Each
> has its own variant of checks for terminating, freezing,
> awakening. In many cases it is unclear to say in which state
> it is and sometimes it is done a wrong way.
> 
> The plan is to convert kthreads into kthread_worker or workqueues
> API. It allows to split the functionality into separate operations.
> It helps to make a better structure. Also it defines a clean state
> where no locks are taken, IRQs blocked, the kthread might sleep
> or even be safely migrated.
> 
> The kthread worker API is useful when we want to have a dedicated
> single thread for the work. It helps to make sure that it is
> available when needed. Also it allows a better control, e.g.
> define a scheduling priority.
> 
> This patch converts the intel powerclamp kthreads into the kthread
> worker because they need to have a good control over the assigned
> CPUs.
> 
> IMHO, the most natural way is to split one cycle into two works.
> First one does some balancing and let the CPU work normal
> way for some time. The second work checks what the CPU has done
> in the meantime and put it into C-state to reach the required
> idle time ratio. The delay between the two works is achieved
> by the delayed kthread work.
> 
> The two works have to share some data that used to be local
> variables of the single kthread function. This is achieved
> by the new per-CPU struct kthread_worker_data. It might look
> as a complication. On the other hand, the long original kthread
> function was not nice either.
> 
> The patch tries to avoid extra init and cleanup works. All the
> actions might be done outside the thread. They are moved
> to the functions that create or destroy the worker. Especially,
> I checked that the timers are assigned to the right CPU.
> 
> The two works are queuing each other. It makes it a bit tricky to
> break it when we want to stop the worker. We use the global and
> per-worker "clamping" variables to make sure that the re-queuing
> eventually stops. We also cancel the works to make it faster.
> Note that the canceling is not reliable because the handling
> of the two variables and queuing is not synchronized via a lock.
> But it is not a big deal because it is just an optimization.
> The job is stopped faster than before in most cases.
> 
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> CC: Zhang Rui <rui.zhang@intel.com>
> CC: Eduardo Valentin <edubezval@gmail.com>
> CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> CC: linux-pm@vger.kernel.org
Tested v3 for functionality and performance, v4 seems unchanged for
this patch according to changelog.

Acked-by: Jacob Pan <jacob.jun.pan@linux.intel.com>

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Thread

[PATCH v4 00/22] kthread: Use kthread worker API more widely Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 21/22] thermal/intel_powerclamp: Remove duplicated code that starts the kthread Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
    Re: [PATCH v4 21/22] thermal/intel_powerclamp: Remove duplicated  code that starts the kthread Jacob Pan <jacob.jun.pan@linux.intel.com> - 2016-01-25 17:30 +0100
  [PATCH v4 18/22] IB/fmr_pool: Convert the cleanup thread into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 03/22] kthread: Allow to call __kthread_create_on_node() with va_list args Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 19/22] memstick/r592: Better synchronize debug messages in r592_io kthread Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 12/22] kthread: Use try_lock_kthread_work() in flush_kthread_work() Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 17/22] ipmi: Convert kipmi kthread into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 08/22] kthread: Initial support for delayed kthread work Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
    Re: [PATCH v4 08/22] kthread: Initial support for delayed kthread  work Tejun Heo <tj@kernel.org> - 2016-01-25 20:10 +0100
  [PATCH v4 01/22] timer: Allow to check when the timer callback has not finished yet Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
    Re: [PATCH v4 01/22] timer: Allow to check when the timer callback  has not finished yet Tejun Heo <tj@kernel.org> - 2016-01-25 19:50 +0100
  [PATCH v4 06/22] kthread: Add destroy_kthread_worker() Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
  [PATCH v4 22/22] thermal/intel_powerclamp: Convert the kthread to kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 16:50 +0100
    Re: [PATCH v4 22/22] thermal/intel_powerclamp: Convert the kthread  to kthread worker API Jacob Pan <jacob.jun.pan@linux.intel.com> - 2016-01-25 17:40 +0100
  [PATCH v4 20/22] memstick/r592: convert r592_io kthread into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 17:00 +0100
  [PATCH v4 15/22] hung_task: Convert hungtaskd into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 17:00 +0100
  [PATCH v4 16/22] kmemleak: Convert kmemleak kthread into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 17:00 +0100
  [PATCH v4 13/22] mm/huge_page: Convert khugepaged() into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 17:00 +0100
  [PATCH v4 14/22] ring_buffer: Convert benchmark kthreads into kthread worker API Petr Mladek <pmladek@suse.com> - 2016-01-25 17:00 +0100
  [PATCH v4 11/22] kthread: Better support freezable kthread workers Petr Mladek <pmladek@suse.com> - 2016-01-25 17:10 +0100
    Re: [PATCH v4 11/22] kthread: Better support freezable kthread  workers Tejun Heo <tj@kernel.org> - 2016-01-25 20:30 +0100
  [PATCH v4 09/22] kthread: Allow to cancel kthread work Petr Mladek <pmladek@suse.com> - 2016-01-25 17:20 +0100
    Re: [PATCH v4 09/22] kthread: Allow to cancel kthread work Tejun Heo <tj@kernel.org> - 2016-01-25 20:20 +0100
  [PATCH v4 02/22] kthread/smpboot: Do not park in kthread_create_on_cpu() Petr Mladek <pmladek@suse.com> - 2016-01-25 17:20 +0100
  [PATCH v4 07/22] kthread: Detect when a kthread work is used by more workers Petr Mladek <pmladek@suse.com> - 2016-01-25 17:20 +0100
    Re: [PATCH v4 07/22] kthread: Detect when a kthread work is used by  more workers Tejun Heo <tj@kernel.org> - 2016-01-25 20:00 +0100
  [PATCH v4 04/22] kthread: Add create_kthread_worker*() Petr Mladek <pmladek@suse.com> - 2016-01-25 17:20 +0100
    Re: [PATCH v4 04/22] kthread: Add create_kthread_worker*() Tejun Heo <tj@kernel.org> - 2016-01-25 20:00 +0100

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