On Wednesday, December 09, 2015 07:34:42 AM Viresh Kumar wrote:
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: Rafael J. Wysocki rafael.j.wysocki@intel.com Signed-off-by: Viresh Kumar viresh.kumar@linaro.org Reviewed-by: Ashwin Chaugule ashwin.chaugule@linaro.org
OK, replaced the one in my tree with this one, thanks!
BTW, can you please add an extra From: line to the bodies of your patch messages?
For some unknown reason Patchwork or your mailer or the combination of the two mangles your name for me and I have to fix it up manually in every patch from you which is a !@#$%^&*() pain.
Thanks, Rafael