[Ardour-Users] ardour3, netjack, bandwidth, xruns

Jörn Nettingsmeier nettings at stackingdwarves.net
Wed Jan 1 08:16:43 PST 2014

hi david,

On 01/01/2014 02:04 PM, David Santamauro wrote:
> Happy new year ... if this isn't the appropriate list, direct to the
> right one, thanks.

you might have more luck on jack-devel for the netjack2-related part of 
your problem.

> I've started creating my orchestral template using ardour3 (on the
> master) and a slave. When I reach a certain number of tracks the xruns
> start piling up.
> Master message(s):
> Wed Jan  1 07:15:08 2014: NetMaster : overloaded, skipping receive from
> 'nslave01'
> ... does this mean the master is overloaded?
> The specs:
>    - master is an 8-core/16GB RAM
>    - slave is 4-core/16GB RAM
> Both have Gb network interfaces and both are connected to a Gb switch.

can you describe what you are trying to do? why do you think you need 
two machines for this task? is the extra complication really necessary 
for the intended job?

> ardour3 does take CPU slices but the master load avg is ~ 85% idle and
> DSP load < 20%.
> Viewing network traffic using iptraf, I see total usage in the 45Mb/s
> (4% utilization) range for both master and slave -- clearly room to
> spare so I'm assuming there is some other bottleneck somewhere.
> There are no xruns on the slave.

just to make sure: only the master has an actual audio interface, and 
the slave's timing comes from netjack2?

> I guess the questions are:
>    - are there hard limits on the number of tracks that can be used when
> using using jack over the network?

no, but i've run into a brickwall at around 100 channels i/o a few years 
ago. since i was using cheap interfaces and didn't actually need more, i 
never tried to pinpoint the problem.

>    - Is there a formula to figure out this out, e.g., is there a
> relationship between the size of the jack graph and data per cycle?

well, 32bit float is four bytes times 48000 times number of channels 
plus packet overhead. even with very small packets (and lots of 
overhead), the network should be able to sustain 300 channels in each 
direction. but of course the entire network stack and netjack would have 
to play along...
how many channels are you actually piping back and forth?

>    - Are there settings (network or for jack_load netmanager) that would
> help this situation?

bigger period size, bigger network packets. for many channels, you might 
want to make sure both ends can use jumbo frames, and of course check 
that there is no MTU bottleneck in between (the switch would have to 
support them as well, fragmentation is deadly for these workloads).

> Both master and slave jackd versions are the same:
> $ jackd -V
> jackdmp
> I've read this [1] and it appears there are two modes: sync and async.
> I'll try toggling this and see what happens.

you should try your luck on jack-devel for these very specific jack2 

hth, best,


Jörn Nettingsmeier
Lortzingstr. 11, 45128 Essen, Tel. +49 177 7937487

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