On 4/10/2013 2:52 AM, Richard Biener wrote:
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.
I have side-stepped the entire -jN issue by using GNU parallel and running
build/test of multiple targets in parallel with each build/test at -j1.
This
doesn't help the per target build time but since we build around 15 targets,
this is an improvement overall.
My rule of thumb is that for builds 1.5-2 times the number of cores is
usually enough to keep a computer occupied but not overwhelmed. But
if you are including running tests on simulators, the cores are heavily
utilized during the test runs so no more than 1.5 times the number of
cores.
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.
This is a big one for RTEMS targets. powerpc-rtems takes ~1hr at -j1
to build binutils, gcc/newlib, and gdb on a 2.9Ghz i7 without testing.
Most of our targets are around 25min. As the number of multilibs
goes up, there are large variations.
Richard.
--
Joel Sherrill, Ph.D. Director of Research & Development
joel.sherr...@oarcorp.com On-Line Applications Research
Ask me about RTEMS: a free RTOS Huntsville AL 35805
Support Available (256) 722-9985
