[Speex-dev] High CPU usage

[Jeff Wallace]

If you are compiling with SSE and/or SSE2 instructions enabled, you could
consider enabling the floating point "Flush-to-zero" mode and maybe (if
supported on the processor) enable "denormals are zero".  The flush-to-zero
is probably the more important of the two.
http://software.intel.com/en-us/articles/x87-and-sse-floating-point-assists-in-ia-32-flush-to-zero-ftz-and-denormals-are-zero-daz/



On Wed, Sep 23, 2009 at 4:06 AM, Jean-Marc Valin <
jean-marc.valin at usherbrooke.ca> wrote:

> Mark Schilling a écrit :
> > I recompiled with FIXED_POINT and CPU utilization stays below 4%. This is
> a great improvement.
> > So how can I fix this to work with floating point ?
>
> OK, so it looks a lot like a denorm problem. The issue is basically that
> there are filters that decay exponentially, so when the input suddenly
> goes to zero, then the filter's output value becomes smaller and smaller
> until it reaches ~1e-37. At that point, your CPU takes >10x the normal
> time to make calculations (why is beyond me).
>
> Now, the work-around is to prevent some signals from going to exacly
> zero. Have a look at how the VERY_SMALL macro is currently being used.
> It's defined as 0 for fixed-point, but 1e-15f for float. By adding that
> value to the right signal(s), you can prevent denormalized numbers from
> being generated. The key is to find that place or those places. A
> profiler may be able to tell you where the problem happens so you can
> add VERY_SMALL just before that place. I suspect that just doing that at
> the output of the preprocessor may be enough but I'm not sure.
>
> Cheers,
>
>        Jean-Marc
>
>
> > Thanks.
> >
> > Mark
> >
> > -----Ursprüngliche Nachricht-----
> > Von: Jean-Marc Valin [mailto:jean-marc.valin at usherbrooke.ca]
> > Betreff: Re: [Speex-dev] High CPU usage
> >
> >
> > Hi,
> >
> > Sound like it could be the good old denormalised float problem on the
> Intel chips. Just to make sure, can you try compiling in fixed-point
> > (FIXED_POINT) and see if the problem goes away (it's not a fix, just a
> test)? If that's the case, there's probably a few VERY_SMALL's to add to
> some signals.
> >
> > Cheers,
> >
> >       Jean-Marc
> >
> >
> > Mark Schilling a écrit :
> >> Hi,
> >>
> >> I have a curious problem with speex. As long as I'm talking, it takes
> about 2-5% of my CPU. This seems ok.
> >> But as soon as I stop talking, CPU utilization rises to about 30-45% and
> stays there until I start talking again.
> >>
> >> I compiled speex from source and use it with these settings:
> >> - Preprocessor: Denoiser = ON, AGC = ON
> >> - Encoder: ABR = 15000, DTX = 1, Mode = narrowband, Rate = 8000 Hz.
> >>
> >> My platform: Windows XP SP3, MSVS 2008 SP1, 1.8 GHz Core Duo CPU, 2 GB
> RAM.
> >>
> >> Thanks for your help :-)
> >> Mark
> >>
> >
> >
> >
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