[OSM-dev] Why is my renderd capped at 8 threads?

[Karl Wettin]

I'm running render_list to push my setup to the limit and see what changes improves the render time.

Two VMs in the same KVM, one running Postgis and the other mod_tile+renderd+mapnik.
Ubuntu 13.10, Mapnik nightly 2.3 ppa, mod_tile from github just a day ago.
PostgresSQL has 100 max connections
Renderd is capped to 16 threads and the VM has 18 cores.
I'm running a large number (20-40) of  render_list processed with -n 1 each

The mod_tile-VM renderd process is rock steady at 790-798% CPU, so something must be capped to 8 threads, presumably on that VM, but what could it be?

root at modtile2:~# cat /etc/renderd.conf 
[renderd]
num_threads=16
...



		karl