[LAU] Question about DSP/Processor Load and multiproc support

[Aurelien]

On Sun, Oct 11, 2009 at 04:12:05PM +0200, Fons Adriaensen wrote :
> On Sun, Oct 11, 2009 at 02:17:30PM +0200, Aurelien wrote:
> 
> > Perhaps my question is not so-well posed.
> > Let's turn it like this:
> > 
> > How is the DSP load appearing in jack computed, and how does it have to
> > deal with CPU/Memory/whateverphysicalthing load?
> 
> It is the total time taken by all clients to finish
> the processing for one period divided by the period
> time. The actual value returned by Jack and shown 
> in qjackctl and ardour is the maximum of this ratio
> over the recent past.
> 

OK. (btw, how is defined the recent past?)

> This means that if a jack client sleeps for half a
> period time in its process callback (it shouldn't
> do that of course) that will show up as 50% in the
> 'DSP load', even if it doesn't take any real CPU.

OK.

> 
> > Does jack generate an xrun as soon as it reaches 100% DSP load as a
> > "security operation" or is it due to hardware limitation when reaching
> > 100% DSP load?
> 
> The xruns you see when Jack is running on AlSA are 
> reported by ALSA. They are usually not related to
> DSP load but could have all sorts of causes. If you
> have such xruns they will typically show up even 
> without any Jack client being active.

Actually, I do not get any xruns, except when load just comes to 100%. I
work with FFADO (unstable) on a Focusrite Saffire Pro 40, and have a
quad-core machine with 8Gb. I mainly use synth (alsa modular x4),
sooperlooper (2 stereo loopers, 2 mono), tapeutape and some (many) audio
routing. I usually work around 80-85% (without sequencer playing) and 90
% load. But sometimes (really not often), I've got this load increase
and then an xrun. It could be widely sufficient if it wasn't purposed
to play onstage, actually.

> 
> When a process cycle takes too long Jack will detect
> this, and AFAIK remove the client that was active
> when the new period should have started. This client
> may or may not be the one that takes too much time. 
> 

OK.

> Ciao,
> 
> -- 
> FA
> 
> Io lo dico sempre: l'Italia è troppo stretta e lunga.
> 
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-- 
Aurélien