Re: [Jack-Devel] new IIO driver added to jack - large overruns

On Tue, Jan 21, 2014 at 11:48:55PM +1100, Matt Flax wrote:
If so: 

> I have found that jack isn't pulling much cpu time at all when
> operating the iio driver. Top reports that it chews about 3% of the
> cpu power. This suggests that a lot of the delay is coming from
> kernel related servicing of the iio read calls.
> 
> The small overruns can probably be removed by reading from the DMA
> buffer in the background, but I would need to do some form of
> locking and unlocking ... whether it be polling in user space or
> some atomic lock system ...

The usual approach is to be woken up from the kernel whenever some parts
of the buffer (let's say one half for a start) are ready for processing.

This doesn't require locking. Thing is, it's a bit hard to give useful
hints, since you're developing an entirely new driver, that is, only you
know the details.

So as a general advice, here's what you can do:

   1.) Have a look at some PCI ALSA drivers and/or read the ALSA driver
       tutorial. Even if you really don't want to write an ALSA driver,
       you'll at least understand the basic approach taken in jackd.


   2.) If you're dealing with a userspace driver, maybe have a look at
       FFADO and its jackd integration. Note that the FFADO project has
       shown that you really want kernel-level streaming, so userspace
       drivers are generally more headache than necessary.

   3.) Take a shortcut and hire Paul Davis, Clemens Ladisch or Daniel
       Mack. No idea if any of these guys is available for freelancing
       at the moment. They know Linux audio inside out and hence know
       how to do it right.


I don't know your hardware at hand, but unless you have very good
reason, I strongly encourage you to write an ALSA driver. This way, your
audio device would automatically work with jack1 AND jack2, so no need
for porting.


Just my €0.02

-- 
mail: [hidden]  	http://adi.thur.de	PGP/GPG: key via keyserver

1390310507.11620_0.ltw:2,a <20140121132139.GK25242 at ltw dot loris dot tv>