Re: [ANNOUNCE][RFC] plugsched-2.0 patches ...

[Peter Williams]

Con Kolivas wrote:
> Marc E. Fiuczynski wrote:
>
> > Paraphrasing Jens Axboe:
> >
> > > I don't think you can compare [plugsched with the plugio framework].
> > > Yes they are both schedulers, but that's about where the 'similarity'
> > > stops. The CPU scheduler must be really fast, overhead must be kept
> > > to a minimum. For a disk scheduler, we can affort to burn cpu cycles
> > > to increase the io performance. The extra abstraction required to
> > > fully modularize the cpu scheduler would come at a non-zero cost as
> > > well, but I bet it would have a larger impact there. I doubt you
> > > could measure the difference in the disk scheduler.
> >
> >
> >
> > Modularization usually is done through a level of indirection (function
> > pointers).  I have a can of "indirection be gone" almost ready to 
> > spray over
> > the plugsched framework that would reduce the overhead to zero at 
> > runtime.
> > I'd be happy to finish that work if it makes it more palpable to 
> > integrate a
> > plugsched framework into the kernel?
>
>
> The indirection was a minor point. On modern cpus it was suggested by 
> wli that this would not be a demonstrable hit in perormance. Having said 
> that, I'm sure Peter would be happy for another developer. I know how 
> tiring and lonely it can feel maintaining such a monster.

Indeed, the more hands the lighter the load.

Another issue (than indirection) that I think needs to be addressed at 
some stage is freeing up the memory occupied by the code of the 
schedulers that were unlucky not to be picked.  Something like what 
__init offers only more selective.

And the option of allowing more than one CPU per run queue is another 
direction that needs addressing.  This could allow a better balance 
between the good scheduling fairness that is obtained by using a single 
run queue with the better scalability obtained by using separate run queues.

Peter
--
Peter Williams                                   pwil3058@xxxxxxxxxxxxxx

"Learning, n. The kind of ignorance distinguishing the studious."
 -- Ambrose Bierce
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