Introduction

Builds can be made even faster by using more than one computer to do the build. Support for distcc, a distributed compiler wrapper, has been added to msrt. This works by passing the post-CPP processed file across the network to the compile node, which compiles it and returns the object code.

A caching build is supported by a compiler wrapper such as distcc's sister program ccache. This works by passing the post-CPP processed file to the cache. If the file has already been seen it will simply return the previously compiled version if not it will compile it (potentially via distcc) and store the result for future cache hits.

This document explains how to use these features with msrt. Also see this page for how to use distcc and ccache in the context of a test release.

Setup

1. Get the source for distcc and/or ccache from the above links. They are packaged for Debian and possibly for your distribution as well. For distcc you will need to run the distccd daemon on every node that will accept compilation jobs. Each node should be configured with a list of IP numbers from which it will accept jobs.
2. Set up needed environment variables:

   • DISTCC_HOSTS (distcc): This should hold a space separated list of host names that distcc should call on for building. They should all have a homogeneous compiler set. Only gcc/g++ jobs are sent here. Others, in particular rootcint jobs, will still be processed on the localhost.
   • PARALLEL (SRT parallel build): This should be set to something (anything) if you want SRT to do per-file parallel builds. It can be used along with PARALLEL_TOP.
   • PARALLEL_TOP (SRT parallel build): This should be set to something (anything) if you want SRT per-Package parallel builds. It can be used along with PARALLEL.
   • MAXLOAD (SRT parallel build): This is optional and if set the localhost load must be less that the value for make to spawn new parallel threads. This will only cause throttling based on the local system load and thus can cause the other compile nodes to starve for jobs. If the local system is taking to big of a hit, consider leaving it out of the DISTCC_HOSTS list.
3. Set up msrt. This can be done on a per invocation basis or for all invocations by editing the users ~/.msrtrc file. The command line options are:

       -d       (use_distcc)    use distcc
       -c       (use_ccache)    use ccache
       -j       (max_make_jobs) set max make jobs (ie make -j XX)
   

   The ~/.msrtrc file variables (in "()" above) are described:

   # Whether or not to also use ccache.  Use of this is independent from
   # parallel build settings below.  This will speed up re-building of
   # files that were built previously (via ccache) but haven't changed,
   # ie. a "msrt clean && msrt build" command chain.
   
   use_ccache=yes
   
   # Whether or not to also use distcc.  You should externally set
   # DISTCC_HOSTS to the list of hosts to use.  If not set MSRT will set
   # it to localhost, which pretty much negates any speed up.  If you set
   # this then do NOT set CCACHE_PREFIX=distcc.
   
   use_distcc=yes
   
   # Max number of make threads allowed.  A good choice is the number of
   # CPUs available.  If this is >1 you should externally set either
   # PARALLEL or PARALLEL_TOP, or both (any value will do).  If neither
   # are set, MSRT will set both.  You may also want to set MAXLOAD to
   # limit how much the local host gets hammered.
   
   max_make_jobs=6
   

Invocation of msrt

Monitoring distcc parallel builds

Some useful ccache related notes

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