Re: [RFCv6 PATCH 09/10] sched: deadline: use deadline bandwidth in scale_rt_capacity

[Luca Abeni]

On 12/15/2015 01:58 PM, Vincent Guittot wrote:
> On 15 December 2015 at 09:50, Luca Abeni <luca.abeni@xxxxxxxx> wrote:
> > On 12/15/2015 05:59 AM, Vincent Guittot wrote:
> > [...]
> > > > > > So I don't think this is right. AFAICT this projects the WCET as the
> > > > > > amount of time actually used by DL. This will, under many
> > > > > > circumstances, vastly overestimate the amount of time actually
> > > > > > spend on it. Therefore unduly pessimisme the fair capacity of this
> > > > > > CPU.
>
> [snip]
>
> > > The 2nd definition is used to compute the remaining capacity for the
> > > CFS scheduler. This one doesn't need to be updated at each wake/sleep
> > > of a deadline task but should reflect the capacity used by deadline in
> > > a larger time scale. The latter will be used by the CFS scheduler  at
> > > the periodic load balance pace
> >
> > Ok, so as I wrote above this really looks like an average utilisation.
> > My impression (but I do not know the CFS code too much) is that the mainline
> > kernel is currently doing the right thing to compute it, so maybe there is
> > no
> > need to change the current code in this regard.
> > If the current code is not acceptable for some reason, an alternative would
> > be to measure the active utilisation for frequency scaling, and then apply a
> > low-pass filter to it for CFS.
>
> In this case, it's probably easier to split what is already done into
> a rt_avg metric  and a dl_avg metric
Yes, I think this could be the best approach for what concerns the average
utilisation used by CFS.



				Luca
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