Re: Not able to make full use of CPUs for processing speed

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 <[email protected]> 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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