On 21-Mar 15:03, Peter Zijlstra wrote: > On Tue, Mar 21, 2017 at 02:37:08PM +0100, Vincent Guittot wrote: > > On 21 March 2017 at 14:22, Peter Zijlstra <pet...@infradead.org> wrote: > > > For the not overloaded case, it makes sense to immediately update to > > OPP to be aligned with the new utilization of the CPU even if it was > > not idle in the past couple of ticks > > Yeah, but we cannot know. Also, who cares? > > > > does exactly that. Note that the lack of idle time is an exact > > > equivalent of 100% utilized. > > > > > > So even while we cannot currently detect the 100% utilized state through > > > the running state tracking; because averages etc.. we can detect the > > > lack of idle time. > > > > But after how much lack of idle time do we consider that we are overloaded ? > > 0 :-)
If we should use "utilization" this time can be non 0 and it depends for example on how long PELT takes to build up a utilization value which marks the CPU as "overutilized"... thus we already have a suitable time at least for CFS tasks. > Note that utilization is an absolute metric, not a windowed one. That > is, there is no actual time associated with it. Now, for practical > purposes we end up using windowed things in many places, > -- #include <best/regards.h> Patrick Bellasi
