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    cpufreq: governor: replace per-CPU delayed work with timers · 70f43e5e
    Viresh Kumar 提交于
    cpufreq governors evaluate load at sampling rate and based on that they
    update frequency for a group of CPUs belonging to the same cpufreq
    policy.
    
    This is required to be done in a single thread for all policy->cpus, but
    because we don't want to wakeup idle CPUs to do just that, we use
    deferrable work for this. If we would have used a single delayed
    deferrable work for the entire policy, there were chances that the CPU
    required to run the handler can be in idle and we might end up not
    changing the frequency for the entire group with load variations.
    
    And so we were forced to keep per-cpu works, and only the one that
    expires first need to do the real work and others are rescheduled for
    next sampling time.
    
    We have been using the more complex solution until now, where we used a
    delayed deferrable work for this, which is a combination of a timer and
    a work.
    
    This could be made lightweight by keeping per-cpu deferred timers with a
    single work item, which is scheduled by the first timer that expires.
    
    This patch does just that and here are important changes:
    - The timer handler will run in irq context and so we need to use a
      spin_lock instead of the timer_mutex. And so a separate timer_lock is
      created. This also makes the use of the mutex and lock quite clear, as
      we know what exactly they are protecting.
    - A new field 'skip_work' is added to track when the timer handlers can
      queue a work. More comments present in code.
    Suggested-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
    Signed-off-by: NViresh Kumar <viresh.kumar@linaro.org>
    Reviewed-by: NAshwin Chaugule <ashwin.chaugule@linaro.org>
    Signed-off-by: NRafael J. Wysocki <rafael.j.wysocki@intel.com>
    70f43e5e
cpufreq_ondemand.c 17.3 KB