Re: [Lse-tech] Re: Real Time Runqueue

Richard Gooch
2001-11-19T18:24:19Z

Andi Kleen writes:
> On Fri, Nov 16, 2001 at 04:32:24PM -0800, Mike Kravetz wrote:
> > The reason I ask is that we went through the pains of a separate
> > realtime RQ in our MQ scheduler. And yes, it does hurt the common
> > case, not to mention the extra/complex code paths. I was hoping
> > that someone in the know could enlighten us as to how RT semantics
> > apply to SMP systems. If the semantics I suggest above are required,
> > then it implies support must be added to any possible future
> > scheduler implementations.
>
> It seems a lot of applications/APIs do not care about global RT
> semantics, but about RT semantics for groups of threads or processes
> (e.g. java or ada applications). Linux currently simulates this only
> for root and with a global runqueue. I don't think it makes too much
> sense to have an global rt queue on a multi processor system, but
> there should be some way to define "scheduling groups" where rt
> semantics are followed inside. Such a scheduling group could be a
> clone flag or default to CLONE_VM for example for compatibility. A
> scheduling group would also make it possible to support simple rt
> semantics for thread groups as non root. Then one could run a rt
> queue per scheduling group, and simulate global rt run queue or per
> cpu rt run queue as needed by appropiate setup.

We have to continue providing global RT semantics. However, a
non-privileged scheduling class which gives RT-like behaviour within a
scheduling group would be *great*! I've wished for such a facility
myself.

Regards,

Richard....
Permanent: rgooch@atnf.csiro.au
Current: rgooch@ras.ucalgary.ca