I'm trying to understand which of the resource limits defined in
/etc/login.conf apply to dpb(1) and how they are set.

Say, I run "doas dpb", so dpb will use its privilege drop model.
The doas(1) command calls setusercontext(3) to set the resource
limits for the user's login class as defined in login.conf(5).

In this case, dpb(1) will get root's class daemon defaults.
Connections to remote build hosts are made through ssh as root,
again getting root's default limits.  Any child processes that dpb
forks inherit those limits.  Toggling the effective user id, as dpb
does, does not magically change those limits.  Yet, when actual
building happens as user _pbuild, apparently the limits for class
pbuild are in force.  How?

What limits apply to dpb running as log user, _pfetch, _dpb?

I've been given a new set of build machines that have a lot more
cores than the previous ones, allowing for more build jobs.  When
I try to make use of those, dpb starts choking badly.  For instance,
ssh multiplexing to remote hosts breaks down.  I take it that dpb
runs into resource limits, but which ones?

-- 
Christian "naddy" Weisgerber                          naddy@mips.inka.de