[Buildbot-devel] Best way to utilize multiple slaves?

[Ian Zimmerman]

I have multiple builders and multiple slaves, and I want to maximize
the number of builds I get through.  Each builder tortures its host
pretty badly so only one can run at a time on each slave.  I use a
slave lock on the builder to enforce that.  Right now there's a
separate Scheduler for each, but I guess there's no reason why I
couldn't use a single AnyBranchScheduler.

I configured each builder (say B1 and B2) to use multiple slaves (say
S1 and S2), and I was naively expecting that when B1 is running on S1
(taking the S1 instance of the slave lock), and a change for B2 comes
in, B2 will be scheduled immediately to run on S2.  But that doesn't
seem to happen; instead B2 is scheduled to run on S1 as well and waits
for the lock to drop.  The only situation when I get some
parallelism is when 2 changes for B1 come in at the same time,
then one of the builds run on S1 and the other on S2.

So, how can I make this better?  Would using AnyBranchScheduler work?
Or do I need to refactor to use a single builder for everything?

Ian