Date: Fri, 27 May 2005 15:56:44 +0200
Message-ID: <s5hwtpkwz4z.wl@alsa2.suse.de>
From: Takashi Iwai <tiwai@suse.de>
To: Andi Kleen <ak@muc.de>
Cc: Ingo Molnar <mingo@elte.hu>, Sven-Thorsten Dietrich <sdietrich@mvista.com>,
       dwalker@mvista.com, bhuey@lnxw.com, nickpiggin@yahoo.com.au,
       hch@infradead.org, akpm@osdl.org, linux-kernel@vger.kernel.org
Subject: Re: RT patch acceptance
In-Reply-To: <20050527133122.GF86087@muc.de>
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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
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