On Thursday 14 January 2010 02:38:04 Ken Restivo wrote:
Turns out that on my Core2Duo, JACK RACK running
Fons's auto-wah plugin
sucks up 6% CPU even if there is no sound going through it.
I asked Fons about it; he can't duplicate the problem since he doesn't have
a 64-bit system. Hell, I can't even duplicate it on my 32-bit system; it's
64-bit dependent.
I looked at the output with Bitmeter at Fons' suggestion, and it seems
there are no denormals, inf's, or nans-- just a very small -230dB DC
offset in the code (probably to avoid denormals).
The CPU usage ramps up before any signal is fed into the plugin. It runs
normally when there is signal, but then it keeps sucking up CPU
afterwards. I'm feeding it from fluidsynth, and bitmeter says that it
isn't sending anthing at all during silent moments.
It doesn't run away to 99% CPU (or 50% on a Core2Duo), like it would if
there were a denormal. But still, why is it using up CPU when there's no
signal? That seems odd. And why only on my 64-bit machine? FWIW, the
64-bit and 32-bit machines I have are even running the same kernel and
RT-patch versions (2.6.26.8-rt12).
Here is a shot:
Maybe the 64bit is better at calculation and -230dB are not yet good enough to
avoid denormals. What if you change that code to add a bit more offset?
Or use it in an ardour session for testing and try the different denormal modes
of ardour to see if one helps...
Have fun,
Arnold