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[fluid-dev] ALSA driver consuming too much CPU

From: Paul Millar
Subject: [fluid-dev] ALSA driver consuming too much CPU
Date: Thu, 16 Nov 2006 18:45:08 +0000
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Hi all,

Inspired by Nathan Harrington's article on monitoring computers with 
FluidSynth (recently linked to from Slashdot), I've started coding against 
FluidSynth's C-library: libfluidsynth.

I'd like to say first how easy it was: libfluidsynth is a very nice library!

The main reason for writing is I've noticed a problem with the ALSA driver.

Pretty much as soon as I do new_fluid_audio_driver(), I see 100% CPU usage.  I 
see this both on my elderly laptop (P3-733MHz) and slightly less elderly 
desktop (P-4 1.7GHz).  Despite the differences in CPUs, in both cases the 
audio sounds OK.

If I use the OSS driver (which, I presume, ALSA is emulating) then the CPU 
load is vastly reduced (i.e. I have some spare CPU cycles!).

The desktop is running Debian testing (kernel: 2.6.17-2-686, libasound2: 
1.0.13-1).  The laptop is running Debian sid.  I don't have access to it 
right now, but it should be running 2.6.18-2-686 kernel package and the same 
version of libasound2 library.

My code uses audio.period-size = 10000 and audio.periods = 10000 by default, 
simply because those were the values used in the Nathan's article.

If it helps any, my code has two files that interfaces with libfluidsynth: 
interface.c (mostly initialisation) and conductor.c (which starts and stops 
notes).  The files are available from:

So, is there anyway I can "turn down" the CPU usage?
(both in general, and for the ALSA driver).



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