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Parallel builds across makefiles

From: thutt
Subject: Parallel builds across makefiles
Date: Thu, 14 Jul 2016 20:26:31 -0700

sgardell writes:
 > We are using a standard distro of gmake 4.1 on RH 6.4.
 > We have a fairly well structured makefile system that leverages the ACE make
 > framework. A linear build (-j1) is about 3 hours. Running a parallel build
 > that builds leaf nodes (libraries) in parallel is about 1 hour. So far so
 > good.
 > But when I try to build across makefiles in parallel then I see two
 > different things:
 >    1) If I turn on any sort of output sync it gets dramatically slower.
 > Sometimes slower than our -j1 time!
 >    2) Even with output sync turned completely off there is no meaningful
 > improvement over a parallel build of just the leaves.
 > I am reasonably certain that I am actually seeing parallel build behavior
 > since I had to fix a handful of additional dependency issues to get it to
 > build. Also reasonably certain that the build is not doing different things
 > since the count of compiler invocations matches. Looking at 'top' during the
 > "highly parallelized" runs shows the system essentially idle.

 Is there a question or problem that you're posing?

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