Re: RT patch acceptance

Ingo Molnar
2005-05-30T10:36:03Z

* Andi Kleen <ak@muc.de> wrote:

> > Yes, as Ingo stated many times, addition cond_resched() to
> > might_sleep() does achieve the "usable" latencies -- and obviously
> > that's hacky.
>
> But it's the only way to get practial(1)low latency benefit to
> everybody - not just a few selected few who know how to set the right
> kernel options or do other incarnations and willfully give up
> performance and stability.
>
> It is basically similar to why we often avoid kernel tunables - the
> kernel must work well out of the box.
>
> (1) = not necessarily provable, but good enough at least for jack
> et.al.

FYI, to get good latencies for jack you currently need the -RT tree and
CONFIG_PREEMPT. (see Lee Revell's and Rui Nuno Capela's extensive tests)

In other words, cond_resched() in might_sleep() (PREEMPT_VOLUNTARY,
which i announced Jul 9 last year) is _not_ good enough for
advanced-audio (jack) users. PREEMPT_VOLUNTARY is mostly good enough for
simple audio playback / gaming.

Ingo