Re: [linux-audio-dev] terrible latencytest results.. why??

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Subject: Re: [linux-audio-dev] terrible latencytest results.. why??
From: Roger Larsson (roger.larsson_AT_norran.net)
Date: Fri Nov 09 2001 - 16:02:50 EET


On Friday 09 November 2001 09:35, Maarten de Boer wrote:
> Roger Larsson <roger.larsson_AT_norran.net> wrote:
> > They are not bad either... (sub 10 ms)
>
> I think it is bad. I want the <3 ms :-)
> I will be added latency in the processing (fft, ifft)
> and it all adds up.
>
> > > Something is definitely very wrong here. I am running kernel
> > > 2.4.13 patched with preempt-kernel-rml-2.4.13-2.patch
> >
> > And you have enabled it in .config? (checking the obvious...)
>
> Yeah, I triple checked the obvious (also: did I run lilo, did
> lilo use the right vmlinuz)
>
> > But wait... an AMD....
> > They have some 3DNow specific kernel optimizations that causes trouble -
> > they need to disable preemtion (uses fp registers...)
>
> Hmm.. Does anybody have more information about this? Could I disable these
> optimizations compiling for another CPU (386, or maybe even Pentium
> Classic?) I suppose the performance penalty that would give would be
> acceptable. Latency is more important.
>

Check if you have this in .config

CONFIG_X86_USE_3DNOW=y

> Would Andrew Morton's LL patches also be affected by this?
>

Yes, if this is the problem.

/RogerL

-- 
Roger Larsson
Skellefteċ
Sweden


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