Re: [Jack-Devel] jack dsp load calculation

On Sat, Dec 26, 2015 at 1:56 PM, Robin Gareus <[hidden]> wrote:

> On 12/23/2015 09:20 PM, John Emmas wrote:
> > On 23 Dec 2015, at 15:35, Robin Gareus wrote:
> >
> >> Hi all,
> >>
> >> I'd like to propose changing the algorithm how jack calculates the DSP
> >> load from averaging to worst-case.
> >>
> >> The main reason for having DSP load is to know how much more processing
> >> one can safely add without getting x-runs. What matters in this case is
> >> the worst-case value.
> >>
> >
> > Matters to whom..?
>
> Those who want to know the peak DSP load and available headroom.
>
> The average is meaningless in the context of DSP. A system may run
> without x-runs 99% of the time but then some NMI or SMI comes along and
> ruins it all. Nobody cares if the average is below 50%.
>
>
For what it's worth, Radium reports three values: 1. Minimum CPU measured
for a block during the last second, 2. Average CPU usage during the last
second,
3. Maximum CPU usage measured for a block during the last second
( http://folk.uio.no/ksvalast/radiumcpu.png )

All three values are useful, at least for me as a developer of the program,
but I guess the users might find all three values interesting as well. At
least
the user doesn't have to wonder whether it's showing peak or average
values, and what the average/peak values would have been if only one
of them had been shown. I guess peak value is the most useful value,
but by showing average and minimum as well, we also indicate the potential
performance the program can deliver without xruns. This potential
can be used by the user to close other programs and do other operations
that might make the computer perform better.

One thing I'm not quite sure of, which is always apparent because all the
values are visible, is why there is such a large difference between
minimum and maximum CPU usage. It's usually at least 4-10
percentage points. I hope it's because of measurement
errors.

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