Re: [RFC][PATCH v2 2/2] cpufreq: schedutil: Avoid decreasing frequency of busy CPUs

[Patrick Bellasi]

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 <peterz@xxxxxxxxxxxxx> 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