Re: RT patch acceptance

[Ingo Molnar]

* Andi Kleen <ak@xxxxxx> 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
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