Re: [Jack-Devel] jack consuming large amounts of CPU time

Hi undersys,

On 10/23/2012 08:11 AM, undersys wrote:
> Hi All,
> 
> I hope someone can give me some guidance with Jack.
> 
> I have Jack set up. All seems to work fine. I can record and playback fine etc.
> My issues starts when I leave Jack running and not doing anything.
> 
> It eats CPU % continually. Making my system quite overloaded until I restart Jack. 

Is it just jackd or are there any jack-clients active when this happens?
e.g. some reverb effects that just process silence..

> Is there something I can check or do? 

yes, and most likely yes.

> I'd really like to have jack running all the time if possible.

[..]
> Device :- Roland Edirol UA-25EX

Is this device directly connected to the PC or is there a USB hub in
between? Is it the sole device on the USB-port?

This is an unusual problem - never heard of it, so you have to provide
more information. With what parameters do you start jackd ('ps axwu |
grep jackd' will tell, or you can copy/paste it from qjackctl's log
window if you use qjackctl to launch jack). What kernel are you running
('uname -a').

Run top and see if it's indeed jackd that has the high CPU load and not
some jack-client.


Some more advanced methods which may or may not make sense:

You can launch jackd in verbose mode and check its log.

Run 'htop'. That can display CPU usage per process and thread as well as
process priority. -> find out if it is indeed jackd itself and its RT
thread (sched fifo, negative priority number) that causes the issue.

check 'cat /proc/interrupts' if your USB interface shares an IRQ with
some other devices..


and some shots in the dark:

Maybe some power-saving kicks in. In particular CPU halt states and/or
bus freq scaling don't go well with jackd. Disable them in the BIOS
(look for sth like EIST, C1E-halt states).

If that does not help, disable CPU freq scaling (not in the BIOS, but on
the system; replace the Linux 'ondemand governor' with the 'performance
governor') - it depends on your distribution and desktop env how to best
do that..

Cheers!
robin

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