[Ardour-Users] Fedora 15 prime for Audio production?

[Robin Gareus]

On 05/28/2011 07:19 PM, Fernando Lopez-Lezcano wrote:
> On 05/26/2011 08:47 PM, George Vergis wrote:
>> Fedora 15 has officially been released as of May 24th. This version
>> includes a
>> Kernel with BKL (Big Kernel Lock) removed. From what I have read you
>> no longer
>> need the real-time kernel patches. Wow! what a relief.
>
> Where have you read this? Could you please post a url?


The BKL has essentially been removed from the core of the kernel and
most drivers since 2.6.29. It's an ongoing project to clean up _all_
drivers and it will likely never be removed completely (e.g. some legacy
serial interfaces). But the BKL is/was only partly responsible for
causing x-runs:

2.6.39 does include the futex, plist and threaded-IRQ handlers from
Thomas Gleixner's RT patch (which more important from an low-latency
audio POV than the BKL removal - however it would not have been possible
to add those without addressing the BKL first).
http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.39

Basically all that's needed for low-latency pro-audio is now available
in the vanialla kernel. YAY.

Note, you need to compile the kernel with
 CONFIG_IRQ_FORCED_THREADING=y
 CONFIG_PREEMPT=y
and also use the kernel-boot-option 'threadirqs' to make use of it.

All in all the task to set-up and tweak a reliable low-latency system
has _not_ become easier. One of the major advantages though is that we
don't need to wait for the rt-patch being forward ported to every new
kernel-release. A task which is currently somewhat stuck at 2.6.33/4.


> While the stock kernel is much better these days than it used to be, and
> is usable for audio work, it is certainly not as good as an rt patched
> kernel. 2.6.39+ will be much closer as it has threaded interrupts. FC15
> ships with 2.6.38.
> 
> Whether you need an rt patched kernel or not depends on the kind of
> audio work you do and the latencies you need to work with (and the
> reliability you expect from the system).
> 
>> However, there are some
>> other user permission settings required to make the audio performance
>> (latency)
>> equal or better than the real-time kernel
> 
> Latencies are not going to be "better than the real-time kernel", at
> least not for 2.6.38 (AFAIK).
> 
> The only thing you should need to do is to install
> jack-audio-connection-kit and then add your user to the proper group
> (that would be "jackuser"). That should be enough to run jack with "-R"
> and get the benefits of realtime scheduling.
> 
> -- Fernando
> 
> 
>> Question: Has anyone managed to get JACK, ardour working on Fedora 15
>> (specifically kernel without BKL), if so, how does the performance
>> compare.

*Performance* is going to be worse with PREEMT_RT for sure. There's
added overhead due to RT scheduling. But you can achieve a *reliable*
low-latency system.

>> Also, if you know of any "HOWTO documentation", especially for Fedora
>> 15, please
>> pass it along.
>>
>> Thanks
>> George
>>
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