If you tell me where most of the denormals are happening, I may be able
to fix that. Also, can you try just adding VERY_SMALL to the encoder's
input and see what happens?
Jean-Marc
Mark Schilling a ?crit :> Hi Jeff,
> Hi Jean-Marc,
>
> I first modified the FPU control word to raise an exception whenever a
denormal is used. Then I used the debugger to locate the exceptions and added
VERY_SMALLs where they seem to fit well.
>
> Although I got CPU usage as low as 10%, I seriously lack knowledge of how
things work inside speex. So just changing some code is not the best idea for
me.
>
> My second attempt was to follow Jeff's suggestion to modify the MXCSR
register and recompile with _USE_SSE. This works very well (CPU < 3%).
>
> However I would still prefer the first method (VERY_SMALL) because not all
CPUs, my app is going to run on, have the SSE instruction set available.
Hopefully someone with more insight is able to fix this some day :-)
>
> Thanks
> Mark
>
>
> -----Urspr?ngliche Nachricht-----
> Von: speex-dev-bounces at xiph.org [mailto:speex-dev-bounces at xiph.org]
Im Auftrag von Jeff Wallace
> Betreff: Re: [Speex-dev] High CPU usage
>
>
> 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 ?crit :
>
> > 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
> >
> > -----Urspr?ngliche 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 ?crit :
> >> 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
> >>
> >
> >
> >
>
> _______________________________________________
> Speex-dev mailing list
> Speex-dev at xiph.org
> http://lists.xiph.org/mailman/listinfo/speex-dev
>
>