[linux-audio-user] Shaving CPU cycles

Ken Restivo ken at restivo.org
Thu Feb 1 18:06:53 EST 2007


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On Wed, Jan 31, 2007 at 10:52:50PM -0500, Ross Vandegrift wrote:
> On Wed, Jan 31, 2007 at 02:25:26AM -0800, Ken Restivo wrote:
> > 2) Try DRM or some kind of accelerated graphics for Xorg
> 
> This might make the problem worse.  Many graphics cards are mean to the
> PCI bus.  The extra interrupts can make latency issues worse.

This is getting really frustrating. I'm getting shunted from pillar to post by conflicting advice from all sides. I'm lost in the ambiguity. This is a "Intel Corporation Mobile 945GM/GMS/940GML Express Integrated Graphics Controller". How would I find out if it is one of the "many"?

> 
> What version of fftw is being used on your system?  If you're using
> fftw v2, make sure to build it for your arch!  If you're using fftw3,
> arch specific SIMD is automatically used by the lib.


$ dpkg -l |grep fftw
ii  fftw2                                  2.1.3-20                        library for computing Fast Fourier Transforms
ii  fftw3                                  3.1.2-1                         library for computing Fast Fourier Transforms
ii  sfftw2                                 2.1.3-20                        library for computing Fast Fourier Transforms

It looks like the only package I have installed that uses it is rezound, which is indeed very slow on my system, but isn't typically in my signal chain.

Interestingly, AMS, which *is* slow and *is* in my signal chain, uses sfftw2 (not sure what's the difference between fftw2 and sfftw2), so I'll definitely try rebuilding it and optimizing it for this CPU (Pentium M, according to kernel config, and vendor_id: GenuineIntel, cpu family: 6, model: 14, according to /proc/cpuinfo).

- -ken
- --

P.S: a handy one-liner for Debian to find which installed packages use fftw2:
	(for i in `apt-cache showpkg fftw2 | grep ','| cut -d, -f 1`; do dpkg -s $i; done 2>/dev/null) |grep Package:
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