[Scons-dev] [Scons-users] Default number of jobs

[Kyle J Strand]

I agree with all of Marc's points, and I'd also like to add that when 
using multiple jobs, Python sometimes crashes (
http://scons.tigris.org/ds/viewMessage.do?dsForumId=1272&viewType=browseAll&dsMessageId=954632#messagefocus
), but I've never observed this with only a single job. So -j1 appears to 
be not only more consistent, but safer.

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Kyle Strand, Software Intern
Beckman Coulter, Inc., Life Sciences Division
4862 Innovation Drive, Fort Collins, Colorado, 80525
(970) 204-7036

scons-users-bounces at scons.org wrote on 07/30/2012 08:25:30 AM:


> Marc Branchaud <marcnarc at xiplink.com> 

> Sent by: scons-users-bounces at scons.org

> 

> 07/30/2012 08:25 AM

> 

> Please respond to

> SCons users mailing list <scons-users at scons.org>

> 

> To

> 

> SCons users mailing list <scons-users at scons.org>

> 

> cc

> 

> SCons developer list <scons-dev at scons.org>

> 

> Subject

> 

> Re: [Scons-users] [Scons-dev] Default number of jobs

> 

> Please don't change the default number of jobs.

> 

> For one thing, not all builds benefit from parallelism.  Ours currently 

> doesn't -- the disk cache gets overwhelmed, even with just a small -j 

> value on a 16-core 32GB machine.  What's more, the optimal level of 

> parallelism (best number of jobs/core) differs from project to project. 

>   Finding the sweet spot is generally a matter of trial, tuning, and 

error.

> 

> More importantly, it can be quite difficult to diagnose problems in 

> parallelized builds, especially since output from simultaneous commands 

> is jumbled together.  Parallel failures of simultaneous commands are 

> especially confusing.

> 

> When developing a build, it's best if your tools don't assume they can 

> do surprising things.  Parallelism is one such surprising thing.  Using 

> an explicit flag to turn it on is a good way for the user to tell the 

> tool that she's ready for some possible weirdness.

> 

>       M.

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