Messages in this thread | | | Subject | Re: cpuidle and cpufreq coupling? | From | Florian Fainelli <> | Date | Thu, 20 Jul 2017 15:56:05 -0700 |
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On 07/20/2017 07:45 AM, Peter Zijlstra wrote: > On Thu, Jul 20, 2017 at 11:52:41AM +0200, Rafael J. Wysocki wrote: >> On Thu, Jul 20, 2017 at 9:18 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote: >>> On 20-07-17, 01:17, Rafael J. Wysocki wrote: >>>> On Thu, Jul 20, 2017 at 12:54 AM, Florian Fainelli <f.fainelli@gmail.com> wrote: >>>>> Hi, >>>>> >>>>> We have a particular ARM CPU design that is drawing quite a lot of >>>>> current upon exit from WFI, and it does so in a way even before the >>>>> first instruction out of WFI is executed. That means we cannot influence >>>>> directly the exit from WFI other than by changing the state in which it >>>>> would be previously entered because of this "dead" time during which the >>>>> internal logic needs to ramp up back where it left. >>>>> >>>>> A naive approach to solving this problem because we have CPU frequency >>>>> scaling available would be to do the following: >>>>> >>>>> - just before entering WFI, switch to a low frequency OPP >>>>> - enter WFI >>>>> - upon exit from WFI, ramp up the frequency back to e.g: highest OPP >>>>> >>>>> Some of the parts that I am not exactly clear on would be: >>>>> >>>>> - would that qualify as a cpuidle governor of some kind that ties in >>>>> which cpufreq? >>>>> - would using cpufreq_driver_fast_switch() be an appropriate API to use >>>>> from outside > > Can your ARM part change OPP without scheduling? Because (for obvious > reasons) the idle thread is not supposed to block.
I think it should be able to do that, but I am not sure that if I went through the cpufreq API it would be that straight forward so I may have to re-implement some of the frequency scaling logic outside of cpufreq (or rather make the low-level parts some kind of library I guess).
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