Messages in this thread | | | Date | Wed, 18 Nov 2015 09:36:22 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH 3/4] sched: introduce synchronized idle injection |
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* Jacob Pan <jacob.jun.pan@linux.intel.com> wrote:
> With increasingly constrained power and thermal budget, it's often necessary to > cap power via throttling. Throttling individual CPUs or devices at random times > can help power capping but may not be optimal in terms of energy efficiency. > Frequency scaling is also limited by certain range before losing energy > efficiency. > > In general, the optimal solution in terms of energy efficiency is to align idle > periods such that more shared circuits can be power gated to enter lower power > states. Combined with energy efficient frequency point, idle injection provides > a way to scale power and performance efficiently. > > This patch introduces a scheduler based idle injection method, it works by > blocking CFS runqueue synchronously and periodically. The actions on all online > CPUs are orchestrated by per CPU hrtimers. > > Two sysctl knobs are given to the userspace for selecting the > percentage of idle time as well as the forced idle duration for each > idle period injected.
What's the purpose of these knobs? Just testing, or will some user-space daemon set them dynamically?
I.e. what mechanism will drive the throttling in the typical case?
> Since only CFS class is targeted, other high priority tasks are not affected, > such as EDF and RT tasks as well as softirq and interrupts. > > Hotpath in CFS pick_next_task is optimized by Peter Zijlstra, where a new > runnable flag is introduced to combine forced idle and nr_running.
> +config CFS_IDLE_INJECT > + bool "Synchronized CFS idle injection" > + depends on NO_HZ_IDLE && HIGH_RES_TIMERS > + default n > + help > + This feature let scheduler inject synchronized idle time across all online > + CPUs. Idle injection affects normal tasks only, yeilds to RT and interrupts. > + Effecitvely, CPUs can be duty cycled between running at the most power > + efficient performance state and deep idle states.
So there are 3 typos in this single paragraph alone ...
I also think that naming it 'idle injection' is pretty euphemistic: this is forced idling, right? So why not name it CFS_FORCED_IDLE?
What will such throttling do to latencies, as observed by user-space tasks? What's the typical expected frequency of the throttling frequency that you are targeting?
Thanks,
Ingo
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