[Scons-users] Not able to make full use of CPUs for processing speed

[Bill Deegan]

Don,

How big is your N?
For reasonable N's SCons can keep up, but for N's in the 100s it' has some
issues.
The folks a MongoDB are using icecc and have built with N's > 250.. and
SCons has issues.
They've floated a PR to address a shortcoming in the scheduler which helped
their build, but it's still marked a WIP so not merged.
see: https://github.com/SCons/scons/pull/3386

You could try making those changes locally and see if that helps.

-Bill


On Wed, Sep 15, 2021 at 3:45 PM Don Baldwin <donb at qti.qualcomm.com> wrote:

> Hi,
>
>
>
> We have a build machine with, say, N CPUs, and we try increasing num_jobs
> to a higher value, but we’re not seeing a decrease in build times.
>
>
>
> For example, say we have 10 CPUs.  We would expect that as num_jobs
> approaches 10, we would continue to see better and better performance
> during the compile phase.  However, what we’re seeing is that performance
> improves until num_jobs hits about 5, at which point further increases to
> num_jobs isn’t having an effect.
>
>
>
> My suspicion is that SCons is doing a lot of processing on it’s own trying
> to figure out which jobs to queue next, e.g. scanning .c files for new
> implicit dependencies, and that there’s a theoretical limit on how many
> CPUs it’s able to keep up with.  Could something like that be going on?
>
>
>
> Thanks,
>
> Don
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