Re: RT patch acceptance

Takashi Iwai
2005-05-27T14:00:38Z

At 27 May 2005 15:31:22 +0200,
Andi Kleen wrote:
>
> On Fri, May 27, 2005 at 03:13:17PM +0200, Ingo Molnar wrote:
> >
> > > > but it's certainly not for free. Just like there's no zero-cost
> > > > virtualization, or there's no zero-cost nanokernel approach either,
> > > > there's no zero-cost single-kernel-image deterministic system either.
> > > >
> > > > and the argument about binary kernels - that's a choice up to vendors
> > >
> > > It is not only binary distribution kernels. I always use my own self
> > > compiled kernels, but I certainly would not want a special kernel just
> > > to do something normal that requires good latency (like sound use).
> >
> > for good sound you'll at least need PREEMPT_VOLUNTARY. You'll need
> > CONFIG_PREEMPT for certain workloads or pro-audio use.
>
> AFAIK the kernel has quite regressed recently, but that was not true
> (for reasonable sound) at least for some earlier 2.6 kernels and
> some of the low latency patchkit 2.4 kernels.
>
> So it is certainly possible to do it without preemption.

Yes, as Ingo stated many times, addition cond_resched() to
might_sleep() does achieve the "usable" latencies -- and obviously
that's hacky.

So, the only question is whether changing (inserting) cond_resched()
to all points would be acceptable even if it results in a big amount
of changes...

Takashi