[Scons-users] Slowness of SCons with a large number of targets

Jason Kenny dragon512 at live.com
Fri Apr 14 20:41:34 EDT 2017

You can pull in Parts. It should help in two different ways.

1) it has a fix to subprocess that should help address the main issues you have.
2) is you use the "part()" concept as well, Parts will help on incremental builds buy reducing what is loaded in memory. This will greatly speed up the builds and time to first build actions.

Hope this helps


-----Original Message-----
From: Scons-users [mailto:scons-users-bounces at scons.org] On Behalf Of Hans Ottevanger
Sent: Friday, April 14, 2017 5:54 AM
To: scons-users at scons.org
Subject: [Scons-users] Slowness of SCons with a large number of targets


At the company I am working for we are revising our software build system and we are currently evaluating build tools. We think that SCons is an interesting tool, offering a high degree of consistency and features that others are clearly missing.

However, we are facing severe performance issues with an increasing number of targets. Experimenting with close to 300000 targets in a tree that mimics a large part of our actual tree, we measured times for a full build of about 35 hours. We just touched the target files and did not invoke real compilers, so those 35 hours are mainly overhead from using SCons.

We are aware of the fact that Eric Melski already reported scalability issues quite some time ago (see https://blog.melski.net/2013/12/11/update-scons-is-still-really-slow/).
We could almost exactly reproduce Erics results using the tools he provides on GitHub (https://github.com/emelski/scons_bench). We are using SCons 2.5.1 and Python 2.7 on VDIs with 4 cores and 16GB RAM and
(perceived) local disk storage, running RHEL6. We need 5000 seconds for 50000 targets, but we see the same quadratic behaviour as Eric Melski reports.

We understand that the issue was diagnosed as being caused by the way Python implements fork() and waitpid() and that relief was expected from a wrapper using posix_spawn(). That stubprocess.py wrapper was slated for inclusion in SCons 2.5, but apparently did not make it (see https://bitbucket.org/scons/scons/wiki/Roadmap).

What are the current plans integrating this stubprocess.py wrapper into an SCons release? And is there already an estimate when we can expect that?

Best regards,

Hans Ottevanger
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