Re: Real-Time Preemption and UML?

Esben Nielsen
2005-02-08T21:20:42Z

On Tue, 8 Feb 2005, Jeff Dike wrote:

> mingo@elte.hu said:
> > Jeff, any objections against adding this change to UML at some point?
>
> No, not at all. I just need to understand what CONFIG_PREEMPT requires of
> UML.

Ingo can probably tell you in much more detail. My problem when I tried to
compile with CONFIG_PREEMPT_RT (not CONFIG_PREEMPT!) was that
__SEMAPHORE_INITIALIZER didn't exist since the architecture specific
semaphore.h is not included in that configuration. The reason again is
that locking (not completions) is changed a lot under CONFIG_PREEMPT_RT to
introduce muteces instead of raw spinlocks and priority inheritance to
make these lockings behave deterministicly.

>
> >From a quick read of Documentation/preempt-locking.txt, this looks like it's
> implementing Rule #3 (unlock by the same task that locked), which looks fine.
>

Now I don't really know who I am responding to. But both up()s now changed
to complete()s are in something looking very much like an interrupt
handler. But again, as I said, I didn't analyze the code in detail, I just
made it compile and checked that it worked in bare 2.6.11-rc2 UML - which
I am not too sure how to set up and use to begin with!

> Jeff
>

Esben