[linux-audio-user] kernel - using rtlimits, realtime_lsm

Josh Lawrence hardbop200 at gmail.com
Wed Dec 21 16:06:18 EST 2005


On 12/21/05, Florian Schmidt <mista.tapas at gmx.net> wrote:
> Well, rtlimits doesn't do this either.
>
> The mechanism to gain realtime privs and the worst case scheduling
> latencies of the kernel are two completely different issues.
>
> For the former, there's the realtime-lsm and rtlimits which _only_
> enable a non root user to do what a root user could do anyways.
>
> For the latter, there's the -rt kernels, although the vanilla kernels
> are quite usable these days, too.

I see, this is exactly the kind of thing I was looking for, and now
that I think about it, it makes total sense.  Let me see if I
understand it:  rtlimits allows a normal user to preempt, but you must
enable the preemption option in the kernel config in the first place
for it to do any good.  Is that it?

> It is quite ok for most uses, especially when not going for ultra low
> latencies (like 8 or 16 frames). Make sure you use the "(X) Preemptible
> Kernel (Low-Latency Desktop)" setting though when building a vanilla
> kernel (or make sure your distro builds it this way if you use a distro
> provided kernel; check i.e. /proc/config.gz and/or write a mail to the
> appropriate ML/maintainer).

Again, this is apparently the part that must be "enabled" to see the
full benefits of using rtlimits, correct?  Once I've enabled this
option (Preemptible Kernel), do I then have what you are referring to
as a -rt kernel?

> Also the -rt kernel, due to prioritizing the irq handler threads,
> provides better RT "guarantees" if you want to call it that ;) I.e.
> given that the scheduler works correct, and that you have setup the
> priorities in your system correctly (and that jackd ant the clients are
> well behaving RT programs), there's almost _no way_ that other system
> activity might cause delays that produce xruns in turn, even with
> ridiculously low latencies.

I don't think that I am the type of user that needs that kind of low
latency, I just need enough to do my basic home recordings.

I think, in light of this, I might install DeMudi on my seperate
partition; it might avoid all of this kernel business very easily.  I
still hate that I don't know how to do things myself, so any further
comment is welcome.

Thank you very much for your comments,

Josh

--
Josh Lawrence
http://www.hardbop200.com




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