Re: [RFC PATCH v2 1/8] sched/cpufreq_schedutil: make use of DEADLINE utilization signal

[Patrick Bellasi]

On 05-Dec 16:24, Juri Lelli wrote:
> On 05/12/17 15:09, Patrick Bellasi wrote:
> > > +	/*
> > > +	 * Ideally we would like to set util_dl as min/guaranteed freq and
> > > +	 * util_cfs + util_dl as requested freq. However, cpufreq is not yet
> > > +	 * ready for such an interface. So, we only do the latter for now.
> > > +	 */
> > 
> > Maybe I don't completely get the above comment, but to me it is not
> > really required.
> > 
> > When you say that "util_dl" should be set to a min/guaranteed freq
> > are you not actually talking about a DL implementation detail?
> > 
> > From the cpufreq standpoint instead, we should always set a capacity
> > which can accommodate util_dl + util_cfs.
> 
> It's more for platforms which supports such combination of values for
> frequency requests (CPPC like, AFAIU). The idea being that util_dl is
> what the system has to always guarantee, but it could go up to the sum
> if feasible.

I see, you mean for systems where you can specify both values at the
same time, i.e.
- please give me util_dl...
- ... but if you have more beer, I would like util_dl + util_cfs

However, I'm not an expert, on those systems can we really set a
minimum guaranteed performance level?

I was more of the idea that the "minimum guaranteed" is something we
can only read from "firmware", while we can only ask for something
which is never "guaranteed".

> > We don't care about the meaning of util_dl and we should always assume
> > (by default) that the signal is properly updated by the scheduling
> > class... which unfortunately does not always happen for CFS.
> > 

-- 
#include <best/regards.h>

Patrick Bellasi