[Ardour-Users] Mixbus32C and more than 200% CPU usage

Paul Davis paul at linuxaudiosystems.com
Thu Jan 11 12:59:55 PST 2018

There's almost no reason whatsoever to measure CPU usage for realtime audio

There's only number that matters: the audio hardware gives you N msec to
process T samples - how close are you to missing that deadline? i.e. if the
hardware gives you 8msec and your system uses 7msec, then any small
disturbance to how long it takes will lead to a dropout ("xrun"). If your
system uses 0.5msec, then there's so much headroom that you can probably
watch a couple of youtube videos and rebuild ardour without worrying about
dropouts. This measure ("DSP Load") is what Ardour and JACK tell you,
instead of some system-based "CPU use" number. If it says "50%" it means
your systems uses half the available time; if it says 1%, it means it uses
1/100th of the available time. On all 3 major OS platforms, xruns start
fairly reliably when this number gets up to about 80%.

Measuring this in terms of "percentage of theoretical CPU cycles actually
used for computing" really misses the point entirely.

On Thu, Jan 11, 2018 at 3:47 PM, jonetsu <jonetsu at teksavvy.com> wrote:

> On Thu, 11 Jan 2018 15:41:59 -0500
> Paul Davis <paul at linuxaudiosystems.com> wrote:
> > are these numbers notably different than previous versions of mixbus
> > on this system?
> Unfortunately this is not something I check.  Only by coincidence while
> looking up something else while Mixbus was running did I notice this.
> You wouldn't perhaps know about Bitwig structure, although for the sake
> of understanding the principle behind this CPU usage, Bitwig takes
> approx. 20% CPU while playing 'many' tracks.  By sketchy comparison, is
> it possible to say that Ardour/Mixbus makes use of all available CPUs
> while the way Bitwig is currently structured does not take these
> resources ?
> Or perhaps, is there a better way to measure true CPu usage for all
> cores ?
> Cheers.
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