Re: [linux-audio-user] Low latency with 2.6.16.16 vanilla

On 5/25/06, Wolfgang Woehl <tito@email-addr-hidden> wrote:
> Wednesday 24 May 2006 02:01, Lee Revell:
> > On Thu, 2006-05-25 at 01:55 +0200, Wolfgang Woehl wrote:
> > > Damn, it doesn't make sense to me. If I can configure the kernel to be
> > > or not to be preemptible then what is the separation good for? Isn't
> > > overhead because of preemption the only price tag?
> >
> > You are confusing preemption (which improves the performance of realtime
> > processes) with the permission to run realtime processes at all
> > (addressed by the realtime LSM, pam, or set_rtlimits).
>
> Err, no. I doubt the need for this restriction. A campus server kernel
> wouldn't be configured for preemption, a dedicated workstation would be. Why
> put another roadblock in the way?

One is a mechanism, useful in many domains. The other controls
who has access to that mechanism. Some systems don't care (yours
pehaps?), others care very much.

There is nothing wrong with this as a system design concept. What
you and many of us are suffering from is the balkanized implementation
of Linux kernels and distributions. The kernel group made some
implementation choices a year ago. While those choices were OK,
they did not worry about all the peripheral pieces needed to gather
them into a useable end-user package. That is not their job.

The required components are now available, and are being provided
by a few leading-edge distributions. Had you installed Ubuntu Dapper
Drake (which is not yet officially released), you would not have seen
any problem. They chose to include the PAM patches and authorize
all users to start realtime threads be default. That is a reasonable
choice for them (given their goals), but would not be appropriate for
most other distributions.

-- 
 joq