Re: [Lse-tech] Separate realtime runqueue

[george a. <ge...@mv...>]

You might want to take a look at:

http://sourceforge.net/projects/rtsched/

Probably more than you want, but...

Seperating the queues shortens the goodness function (it need not check
rt tasks) and should be a win, assuming you don't try to use the same
goodness function on both.

George

Hubertus Franke wrote:
> 
> * Mike Kravetz Wrote
> >
> >
> > I'm in the process of rewriting the MQ patch in the hope that
> > it will be more 'Linus friendly'.  One thing I want to do is
> > keep as much code as possible common between the UP and SMP
> > versions of the scheduler.  In the MQ scheduler, we keep a
> > separate real-time runqueue.  I was wondering if it would make
> > sense to keep a separate real-time queue in the UP case.  I
> > know several people have played with the idea of a separate
> > real-time queue in the past.  Does anyone recall the outcome
> > of this work?
> >
> 
> Mike, these are the issues that will arise.
> (a) if you integrate with the current MQ structure
>     the RT-Q will be on its own cache line, so you would have
>     in general one extra cacheline access and test, whether you
>     have RT tasks or not.
> (b) during add_from_runqueue() and del_from_runqueue() you will
>     still have to distinguish which queue the tasks fall on.
> (c) on the plus side, if you have RT tasks you can probably serve them
>     quicker then running through the whole single queue.
> 
> So all in all, one will encounter a few more instructions under (b) and
> and additional cache hit under (a).
> 
> > In addition, does anyone know of a benchmark that can be used
> > to test 'real-time performance' with respect to the scheduler?
> > I want to make sure we don't degrade the real-time case.
> >
> > Thanks,
> > --
> > Mike Kravetz                                  kr...@us...
> > IBM Linux Technology Center       (we're not at Sequent anymore)
> >
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