On Wed, Apr 10, 2013 at 4:51 AM, Geert Bosch <bo...@adacore.com> wrote: > > On Apr 9, 2013, at 22:19, Segher Boessenkool <seg...@kernel.crashing.org> > wrote: > >> Some numbers, 16-core 64-thread POWER7, c,c++,fortran bootstrap: >> -j6: real 57m32.245s >> -j60: real 38m18.583s > > Yes, these confirm mine. It doesn't make sense to look at more > parallelization before we address the serial bottlenecks. > The the -j6 parallelism level is about where current laptops > are. Having a big machine doesn't do as much as having fewer, > but faster cores.
Indeed having 4-6 cores with the possibility of serial stages letting the CPU boost the only active cores frequency as much as possible leads to the fastest _bootstrap_ times. Now, testing is a different story here - and testing dominates my bootstrap / regtest throughput. So the idea of a combined bootstrap & test make target that would interleaves stage3 target library building, target library testing and compiler testing (harder due to some target library dependencies of certain .exp files) would already help (thinking of how libjava building is the bootleneck for a --enable-languages=all build). Similar allowing to build multilibs in parallell. Richard.
