Re: [Jack-Devel] jack dsp load calculation

On 12/26/2015 10:56 PM, Joakim Hernberg wrote:
[..]

> IME the dsp load is a relatively useless measure as it's not really
> related to the max value (which is where an xrun occurs)..  You could
> very well have a system with a very low dsp load xrunning all the
> time...

exactly.

But if we add a new API, I would not mind if it also included a proper
statistical average (and maybe min,..) since there seems to be interest.

We might as well leave the old jack_cpu_load() code untouched, but I
think it should be changed to report the max.

> Maybe a nice idea would be similar to a mixer meter showing rms and
> peak values, like that everyone could have their cake and eat it too ;)

heh.

> Apart from that there is the xrun callback that indicates that an xrun
> did indeed occur.  If we only had Jack2 to worry about, I'd suggest
> leveraging jack2's excellent profiling code, which can give a very good
> analysis of how the system performs.

JackEngineControl::CalcCPULoad() already uses that API to calculate the
cycle duration.

My criticism is with the built-in pre-processing in that function.

@John: If libjack were to expose both RMS and peak, the client
application - in your case Mixbus - can do the same thing as jack
currently does: Display the max if some conditions are met and the
average otherwise and also filter the value ad lib, so nothing is lost.
It could even be some user-preference..

Do you see some issues with this approach?


@Joakim: Thanks for the reminder about Timing PDF. This shows that at
least on POSIX systems the measurement error is small and that there can
be spikes nearly twice as large of the average value.

Cheers!
robin

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