[ag-automation] neuer Mitleser

[Thomas Gleixner]

On Mon, 2006-04-10 at 10:29 +0200, Jan Kiszka wrote:

> From the user perspective, RTDM adds a small amount of new kernel
> services (like all Xenomai skins) which can both be used by non-POSIX
> skins (native, VxWorks, etc., that's the rt_dev_ interface) or be
> mapped on the original POSIX service as done inside the POSIX stub
> library. [This is how it works under Xenomai and RTAI, but on
> Preempt-RT we would of course use the existing file and socket
> infrastructure.]

Could you please explain the basics of RTDM and how an integration into
mainline (w or w/o rt-preempt) would look like ?

> Not yet, but it seems to be the announcement text. Typically, I prefer a
> code review over documentation, and the aspects I'm referring to (risk
> of -ENOMEM on mutex lock, hash chain lock dependencies on futex look-up,
> tasklist_lock dependencies) were not mentioned in the announcements yet.

This really depends on what you want to achieve. The PI-Futex
implementation is focussed on the optimization of the non contended
case. Enforcing a syscall per lock operation is definitely something you
want to avoid. The original Bull/Intel/MVista patch did exactly this and
its rather simple to figure out whats the overhead.

If you trap into the -ENOMEM situation in the locking code, then your
system has reached its limits anyway.

	tglx