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.