[distcc] speedup with >2 hosts

[Dan Kegel]

SCHMID Stefan wrote:
> i'm using a system of five dual-CPU distcc-hosts for distributed 
> compilation. with all my projects, one additional host is very useful 
> but the third to fifth hardly contribute anything at all. moreover, 
> there is quite some variation in the execution time although all hosts 
> do nothing else besides compilation (maybe because of the sleeping times 
> when hosts are locked?). it is therefore also hard to tell which 
> -j-option is the best for a given number of hosts...
> 
> all in all, with 5 hosts (10 cpu's) i hardly get any speedups greater 
> than 2 (compared to one host, i.e. 2 cpu's). do you have an idea where i 
> do something wrong?
> 
> my test results (secs for execution) for two projects (see 
> http://pool.cern.ch/ and  http://cobra.web.cern.ch/cobra/) 

Are all 5 hosts equal performance?  What kind of systems are they?
What does your DISTCC_HOSTS list look like?

Looks like you're using a strange build system written
in Python called SCRAM.  Are you quite sure that's not
the bottleneck?  None of us, I suspect, have ever heard
of it.

Do check out the notes Benjamin Meyer just posted,
http://www.csh.rit.edu/~benjamin/articles/distcc.php
- Dan

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