About making life easier for audio producers.

[drago01]

On Mon, Feb 16, 2015 at 1:49 PM, Josh Boyer <jwboyer at fedoraproject.org> wrote:
> On Mon, Feb 16, 2015 at 1:50 AM, drago01 <drago01 at gmail.com> wrote:
>> On Mon, Feb 16, 2015 at 6:23 AM, Diogo Campos (gmail)
>> <diogocamposwd at gmail.com> wrote:
>>> You've asked to make it easier but you've made no suggestions or proposals
>>> on how it might be achieved.
>>>
>>>
>>> Sorry if it seemed a random complaint.
>>>
>>> Fact is that I am a victim of this issue, so I really did not feel
>>> comfortable to propose solutions at a technical level.
>>>
>>> Anyway, since you asked:
>>>
>>> 1- Install JACK.
>>>
>>> I think the package would be "jack-audio-connection-kit".
>>>
>>> 2- Set a list of standard and optimized initialization options for JACK.
>>>
>>> Most likely disabling the "realtime" option (with "--no-realtime"), since,
>>> as far as I understand, the Fedora kernel does not have support for it.
>>
>> It does. The thing is that setting real time scheduling for an app is
>> a privileged operation. Jack should use rtkit for that (like
>> pulseaudio does).
>
> The Fedora kernel doesn't carry the -rt patchset, which is what most
> people equate to "realtime" in the Linux world.  I'm not sure what you
> were thinking of here?

Its not about the -rt patches (those would improve things for audio
producers; but that's a different story) but what jack tries to do is
simply set the scheduling policy of the process to SCHED_RR.
Pulseaudio already does this (for the same reason) using rtkit:

"RealtimeKit is a D-Bus system service that changes the scheduling
policy of user processes/threads to SCHED_RR (i.e. realtime scheduling
mode) on request. It is intended to be used as a secure mechanism to
allow real-time scheduling to be used by normal user processes."

So what I suggested is to change jack to use rtkit instead of
requiring setuid or even full root privileges for it. Non of this
require any kernel changes nor the -rt patches.