[PlanetCCRMA] The JACK Story (or "The State of (the Union) JACK" speech)
David Nielson
naptastic at comcast.net
Mon Nov 23 13:09:48 PST 2009
I want to make sure I understand all this correctly.
1. When we are talking about "priority" in this context, are we talking
about which processes have permission to preempt which other processes?
A higher priority task can preempt a lower priority task but not vice-versa?
2. When we talk about "kernel threads" (rtc) are we talking about things
like the scheduler, which should never ever be preempted, or are we
talking about things like disk I/O?
3. Does the system in place distinguish between critical kernel
processes, like the scheduler, and things that a user might want to put
off until later, like disk I/O? (The reason I ask is that, with my
setup, I can get 128x2 to be rock-solid *unless* there is an SD card in
my computer's SD card reader, and if I am copying a file from the SD
card to the hard disk, I get xruns of 40ms (forty milliseconds, REALLY!)
so there is obviously something in the I/O that should get preempted but
doesn't.)
4. Would rt permissions for regular users be unacceptable to regular
Fedora because of the possibility of a user crafting or unintentionally
running a task with a high priority which then crashes, potentially
taking down the entire system?
5. Does it really make that much difference? I know software I can write
and run on a non-rt kernel as a regular user that basically takes down
the entire system for everyone. So what's the big deal?
6. If I understand correctly, the ability of a user to start
high-priority tasks depends on their membership in the jackuser group.
Would it be acceptable to the Fedora people to have a "audio
configuration wizard" applet (forgive me; I grew up with Windows) that
requires the root user to grant membership to the jackuser group, and
includes a Big Scary Warning about the potential for disaster?
(I think it's probably safe to assume that in most DAWs, the end user
and superuser are the same person, but for the average Fedora
installation, that's an unsafe assumption?)
David Nielson
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