[Speex-dev] High CPU usage

[Jean-Marc Valin]

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 écrit :
> 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
> 
> 
> -----Ursprüngliche 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 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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