On 12 February 2016 at 11:15, Rafael J. Wysocki <raf...@kernel.org> wrote: > On Fri, Feb 12, 2016 at 5:01 PM, Rafael J. Wysocki <raf...@kernel.org> wrote: >> On Fri, Feb 12, 2016 at 3:10 PM, Peter Zijlstra <pet...@infradead.org> wrote: >>> On Thu, Feb 11, 2016 at 10:52:20AM -0800, Steve Muckle wrote: >>>> On 02/11/2016 09:30 AM, Peter Zijlstra wrote: >>>> >> My concern above is that pokes are guaranteed to keep occurring when >>>> >> > there is only RT or DL activity so nothing breaks. >>>> > >>>> > The hook in their respective tick handler should ensure stuff is called >>>> > sporadically and isn't stalled. >>>> >>>> But that's only true if the RT/DL tasks happen to be running when the >>>> tick arrives right? >>>> >>>> Couldn't we have RT/DL activity which doesn't overlap with the tick? And >>>> if no CFS tasks happen to be executing on that CPU, we'll never trigger >>>> the cpufreq update. This could go on for an arbitrarily long time >>>> depending on the periodicity of the work. >>> >>> Possible yes, but why do we care? Such a CPU would be so much idle that >>> cpufreq doesn't matter one way or another, right? >> >> Well, in theory you can get 50% or so of the time active in bursts >> that happen to fit between ticks. If we happen to do those in the >> lowest P-state, we may burn more energy than necessary on platforms >> where more idle is preferred. > > At least intel_pstate should be able to figure out which P-state to > use then on the APERF/MPERF basis.
Speaking for the generic case, it would be great to make use of such feedback counters for selecting the next freq request. Use (num of cycles used/total cycles) to figure out %ON time for the CPU. I understand its not the goal for this patch series, but in the future if we can do this in your callbacks where possible, then I think we will do better than Ondemand. Regards, Ashwin. > -- > To unsubscribe from this list: send the line "unsubscribe linux-pm" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
