[Scons-users] [Scons-dev] Default number of jobs

[Marc Branchaud]

Please don't change the default number of jobs.

For one thing, not all builds benefit from parallelism.  Ours currently 
doesn't -- the disk cache gets overwhelmed, even with just a small -j 
value on a 16-core 32GB machine.  What's more, the optimal level of 
parallelism (best number of jobs/core) differs from project to project. 
  Finding the sweet spot is generally a matter of trial, tuning, and error.

More importantly, it can be quite difficult to diagnose problems in 
parallelized builds, especially since output from simultaneous commands 
is jumbled together.  Parallel failures of simultaneous commands are 
especially confusing.

When developing a build, it's best if your tools don't assume they can 
do surprising things.  Parallelism is one such surprising thing.  Using 
an explicit flag to turn it on is a good way for the user to tell the 
tool that she's ready for some possible weirdness.

		M.