[LAU] jack performance in ubuntustudio

[Joakim Hernberg]

On Fri, 25 Jul 2014 06:27:54 -0700 (PDT)
Len Ovens <len at ovenwerks.net> wrote:

> Running ubuntustudio 14.04 here. jackdbus is set 2/32 and I turned 
> pulse->jack bridging on. qjackctl shows DSP at 6-12%, Gnome system
> monitor shows all cores at around 4%, Top shows pulse at 11%, the
> sound card at 6%, jack at 3.5%, a2jmidid at 2%.... turning pulse off
> has top showing the sound card at 8%, jack at 6% and a2j at 2%, but
> jack DSP is 3.5%. All of which brings into question the tools we use
> for measuring this stuff and what those numbers really mean.
> 
> Setting my system to desktop mode (2048 frames, pulse on) gives jack
> dsp of .88% (or less) and makes them harder to follow in top because
> they are now at least fifth down and all less than 1%.

You are comparing apples and oranges :)

Most of those measurements are cpu use, qjackctl's dsp load is a
measure of latency (execution time). That is to say there is a deadline
given by the sample rate divided by the buffer size.  If DSP load is
50%, the audio processing has used up half of the time available.  If
100% it has used up all the time.  Note that there is overhead
involved, the conventional wisdom is to not go over 50%, but ymmw..

-- 

   Joakim