Re: Priority Inheritance Test (Real-Time Preemption)

john cooper
2004-11-23T01:37:45Z

Bill Huey (hui) wrote:
> On Mon, Nov 22, 2004 at 09:16:18AM -0500, john cooper 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. Getting correct behavior and scaling on SMP
>>require some restrictions of how lock ownership is maintained,
>>otherwise fine grained locking is not possible. Another likely
>
>
> What do you mean by that ? Are you talking about strict priority
> obedience by the system ?

Not quite if I understand your question. I was referring to
avoiding having a global lock to synchronize the conglomerate
data structure when doing a PI dependency walk. The problem
is the lock must be acquired not only in PI scenarios but in
any case which may possibly lead to one or affect a concurrent
PI in progress.

True this global lock is mostly an issue for large count
SMP systems. But as witnessed by such voodoo[1] mechanisms
as rcu, scalability problems are real at that end of the
spectrum.

-john

[1] in a 'nice' way.

--
john.cooper@timesys.com