Re: [PATCH] Priority Lists for the RT mutex

[Sven-Thorsten Dietrich <sdietrich@mvista.com>]

On Fri, 2005-04-08 at 08:28 +0200, Ingo Molnar wrote:
> * Daniel Walker <dwalker@mvista.com> wrote:
> 
> > 	This patch adds the priority list data structure from Inaky 
> > Perez-Gonzalez to the Preempt Real-Time mutex.
> 
> this one looks really clean.
> 
> it makes me wonder, what is the current status of fusyn's? Such a light 
> datastructure would be much more mergeable upstream than the former 
> 100-queues approach.

Ingo,

Joe Korty has been doing a lot of work on Fusyn recently.

Fusyn is now a generic implementation, similar to the RT mutex. SMP
scalability is somewhat better for decoupled locks on PI (last I
checked). It has the extra bulk required to support user space.

The major issue that concerns the Fusym and the real-time patch is that
merging the kernel portion of Fusyn creates a collision of redundant PI
implementations with respect to the RT mutex.

The issues are outlined here:

http://developer.osdl.org/dev/mutexes/

There are a few mistakes on the page, (RT mutex does not do priority
ceiling), but for the most part the info is current.

If the RT mutex could be exposed in non PREEMPT_RT configurations,
the fulock portion could be superseded by the RT mutex, and the
remaining pieces merged in. Or vice versa.

We discussed the scenarios recently, any guidance you can offer to help
us out would be greatly appreciated.

http://lists.osdl.org/pipermail/robustmutexes/2005-April/000532.html


Sven