RE: [RFC/PATCH] FUSYN Realtime & robust mutexes for Linux, v2.3.1

[Perez-Gonzalez, Inaky]

> From: Andrew Morton [mailto:akpm@xxxxxxxx]
> 
> Ulrich Drepper <drepper@xxxxxxxxxx> wrote:
> >
> > Andrew Morton wrote:
> >
> > > This fixes what appear to be some fairly significant shortcomings.  What do
> > > the futex and NPTL people have to say about the gravity of the problems
> > > which this solves, and the offered implementation?
> >
> > This code will not be suppoerted by the glibc code.  Using these
> > primitives would mean significant slowdown of all operations and this
> > for problems which only a few people have.
> 
> How large is the slowdown, and on what workloads?

10% on volanomark, as well in some other conditional variable stress
tests we have been conducting. For the conditional variable one we have
an initial proof of concept optimization that we'll try in a couple weeks
[I am going on vacation next week].

> >  I asked to get the useful
> > parts of the code to be made available using the current futex interface
> > (robust mutexes are useful)
> 
> Passing the lock to a non-rt task when there's an rt-task waiting for it
> seems pretty poor form, too.

???? That never happens in fusyn [unless there is a bug]. The next guy who 
gets the lock if it is being passed (or is woken up) is always the highest 
priority one.

Iñaky Pérez-González -- Not speaking for Intel -- all opinions are my own (and my fault)
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