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Re: parallel make

make -j does work in cygwin, to an extent. If you try to use too many processes, cygwin seems to flip out. -j20 does seem to work fine though (it only starts acting strang around -j100).

On my large build system, we have a slow disk, and I find that when the disk cache is empty, -j4 speeds it up about 40%. When the build system is cached, -j slows things down by a few percent. This is dealing with 1 processor. Of course, if you have multiple processors, the speed should scale linearly (with 4 cpu's, -j4 is about 70% faster).

Rich Elberger wrote:

Hi folks,
Currently our build environment uses parallel make (-j jobs option) on all
our unixes using gnu tools.  We use an older version of gnu tools on our
windows boxes.  The older make on the windows box does not do parallel
make (or at least correctly).  I want to upgrade to the latest cygwin to
see if parallel make works, but this will require significant changes to
our build engine, so I would like to confirm a few things if possible.

1. Does the -j jobs option work well on windows. (part b: does it work
with the MSVC (6/7) compiler (which probably doesn't make a difference
2. Has anyone done this in a very large project, and if so, do you have
any performance gain stats (which, I acknowledge, is tied to
processor-intensive makes and how many processors the machine has).

I realize that dos does not allow for threading so I don't know if this is
a cmd.exe-related issue or not (since cmd.exe is the parent shell, I
don't know if this affects the behavior).

thanks in advance --

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