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

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.

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.

> 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.

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.

Ciao,

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