Re: Priority Inheritance Test (Real-Time Preemption)

Ingo Molnar
2004-11-23T08:20:25Z

* john cooper <john.cooper@timesys.com> wrote:

> >>I'd hazard a guess the reason existing implementations do not do this
> >>type of dependency-chain closure is the complexity of a general
> >>approach. [...]
> >
> >
> >please take a look at the latest patch, it is i believe handling all the
> >cases correctly. It certainly appears to solve the cases uncovered by
> >pi_test.
>
> Yes I see where you are walking the dependency chain
> in pi_setprio(). But this is under the global spinlock
> 'pi_lock'.
>
> My earlier comment was of the difficulty to establish fine
> grained locking, [...]

the issues raised in the paper and in this thread were much more
fundamental than SMP-scalability. Considering the costs of a hard-RT
mutex approach itself i dont think SMP-scalability is a primary issue
right now.

> [...] However I'd offer there is more concurrency possible in this
> design.

yeah, most likely - but correctness comes first. SMP scalability is
something that can be done later.

Ingo