[linux-audio-user] Problems appling realtime preempt patch to 2.6.12 (general)

Fernando Lopez-Lezcano nando at ccrma.Stanford.EDU
Wed Jul 13 16:12:14 EDT 2005


On Wed, 2005-07-13 at 08:09, Eric Dantan Rzewnicki wrote:
> On Tue, Jul 12, 2005 at 01:46:13PM -0700, Fernando Lopez-Lezcano wrote:
> > On Tue, 2005-07-12 at 12:56, Iain Duncan wrote:
> > > >>I've just joined the list and it's pretty interesting.
> > > >>Can someone tell me something about the differences between the
> > > >>preempt patch from Ingo and the "Realtime Linux Security Module"?
> > > >>I currently use the latter one and I'm quite satisfied as jack works
> > > >>really fast. Perhaps one should try this way instead of the vanilla
> > > >>kernel patch. There have to be pros and cons I'm interested in. Can
> > > >>someone point them out? 
> > > > The LSM and Ingo's patches are addressing 2 separate issues. Ingo's
> > > > patch is working to minimize sources of latency in various code paths in
> > > > the kernel. The rtlimits and the realtime-lsm are addressing the issue
> > > > of providing a security model for realtime applications to get the
> > > > capabilities they need to run in real-time. Ordinarilly these
> > > > capabilities (CAP_SET_PCAP, mlockall(), and SCHED_FIFO()) are only
> > > > accessible as root. rtlimits and the realtime-lsm provide infrastructure
> > > > for allowing these capabilities to be granted to only a specified set of
> > > > users/processes.
> > > So am I correct in believing that the preempt patch is the one that 
> > > makes a difference if I intend to run as root anyway?
> > It makes (should make?) a difference independent of whether you run as
> > root or not. If you run as root you can access everything. If you don't
> > run as root (highly recommended :-) you need some additional stuff to
> > get the same performance.
> > > ( Yeah I know I'm 
> > > not supposed to, but IMO my machine is just a synthesizer in disguise as 
> > > a computer and I'll unplug the ethernet cable if I need to. )
> > 2.6.12 already includes the rlimits patch that will allow you to run
> > well as a non-root user. But you will need a patch to pam (if your
> > distro uses pam) or a special user program to access realtime scheduling
> > as a non-root user (was posted not long ago to this list).
> 
> I vaguely recall that demudi stuck with the realtime-lsm for the current
> version. Is this correct?
> 
> Are there deb packages of the patched pam available? 
> what about rpm's for ccrma?

The latest "edge" kernels on Planet CCRMA (for fc3/fc4) use rlimits and
the repository includes a matching patched pam...

-- Fernando




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