If you had a month to improve gcc build parallelization, where would you begin?

[Geert Bosch]

On Apr 3, 2013, at 23:44, Joern Rennecke <joern.rennecke@embecosm.com> wrote:

> How does that work?
> The binaries have to get the all the machines of the clusters somewhere.
> Does this assume you are using NFS or similar for your build directory?
> Won't the overhead of using that instead of local disk kill most of the
> parallelization benefit of a cluster over a single SMP machine?

This will be true regardless of communication method. There is so little
opportunity for parallelism that anything more than 4-8 local cores is
pretty much wasted. On a 4-core machine, more than 50% of the wall time 
is spent on things that will not use more than those 4 cores regardless.
If the other 40-50% or so can be cut by a factor 4 compared to 4-core
execution, we still are talking about at most a 30% improvement on the 
total wall time. Even a small serial overhead for communicating sources
and binaries will still reduce this 30%.

We need to improve the Makefiles before it makes sense to use more
parallelism.  Otherwise we'll just keep running into Amdahl's law.

  -Geert