BuildConfiguration.xml - PCH & MaxParallelActions question

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1

Hello,

I had a question related to building Unreal from source related to PCH and the buildconfiguration.xml

I’ve added the following to the buildconfiguration.xml file:

<?xml version="1.0" encoding="utf-8" ?>
<Configuration xmlns="https://www.unrealengine.com/BuildConfiguration">
    <BuildConfiguration>
        <bUseUnityBuild>false</bUseUnityBuild>
        <bUsePCHFiles>true</bUsePCHFiles>
        <MaxParallelActions>64</MaxParallelActions>
    </BuildConfiguration>
    <ParallelExeuctor>
        <ProcessorCountMultiplier>2</ProcessorCountMultiplier>
        <MaxProcessorCount>64</MaxProcessorCount>
    </ParallelExeuctor>
</Configuration>

So, a few questions:

  • The number of threads reported is 128, but the MaxParallelActions being set to 128 causes the machine to crash every build, setting this to 64 resolves this issue. As this machine is on Win 10 21H2, the group1 of the 3990X seems to not be active when building from VS2022. Is MaxParallelAction relating to physical core count, or to threads?
  • When building from source, with PCH enabled via the buildconfiguration.xml there is 32040 files to build, and with PCH disabled there is 5749. Do PCH files compile on the first build, and then reference the PCH files after or until a rebuild is initiated?

Thanks for any insights! :grin:

2

Solved my own issue, was UnityBuild being disabled, it was not concatenating builds.