[LAU] Performance tuning audio apps -- Success!

Ken Restivo ken at restivo.org
Mon Aug 17 18:30:30 EDT 2009


I ended up using the following flags:

-msse -msse2 -mfpmath=sse -ffast-math -fomit-frame-pointer -O3 -fno-finite-math-only -pipe

And all is well. I can run azr3, two fluidsynths, jackd, lashd, jackminimix, linuxsampler (!), and four jack-rack instances with plugins from CAPS, TAP, CALF, and Fons's autowah, and play them with responsiveness and no glitches... on a dinky little Atom 1.6Ghz netbook... while compiling software and running Firefox. Yay Linux!

Fluidsynth through jack-rack seems a lot more responsive too; less latency, even though latency was already quite low. The exception here is LinuxSampler which has a little  bit of a lag, understandably.

Couple issues:
1) At Fons's suggestion, I had to add "LDFLAGS += -shared -nostartfiles" to the debian/rules of CAPS 0.4.3 to get it to build.

2) Fluidsynth is acting very strangely. It "gets jealous". If I'm playing another synth, which is demanding a lot of CPU, Fluidsynth throws a tantrum and sucks up spikes of 80% CPU (according to top). AZR3 does this too sometimes. Why is that? Why would a synth be sucking up tons of CPU even if no MIDI data is going into it? Is it getting starved by the others.

3) Volume levels on AZR3 are sane now, for the first time ever, which suggests maybe it had a denormal issue in there which one of those optimization flags might have fixed.


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