On 10/8/2010 11:57 AM, kent williams wrote:
I think what I'm doing isn't clear to you.
I have a CMakeLists.txt that is essentially 'sourceless' -- it defines
a bunch of CMake variables, and then builds a bunch of prerequisites
and applications added with ExternalProject_add. It doesn't have any
add_subdirectory,add_executable, add_library etc of its own.
So at build time, the process tree is
make # the make of the top level
make # build external project 1
.
.
make # build external project n
If I use make -j4, for example, it would build 4 external projects in
parallel with make -j1. If any of those projects is on the critical
path, and takes significantly longer to build than any other projects,
the build process bottlenecks doing the sequential build of that one
project.
My method -- changing the build command for the external projects to
use -j4 for example, will instead do a sequential series of parallel
sub-makes, instead of a parallel series of sequential submakes.
I've tried it both ways and this is how it works.
We have fixed things recently to address this. The way it should be
working:
make # top level
make # build external project 1
.
.
make # build external project n
make -j4 at the top:
The make jobserver should take care of the rest and make sure that 4
different things are always building at the same time. This could be
.o files from more than one external project if that is how it works out.
This is possible because $(MAKE) is used so when the external projects
are run gmake will pass the jobserver information down to the next
sub-make. The jobserver will keep track of making sure no more than 4
things are running at the same time.
-Bill
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