[Scons-users] SCons very slow on GitHub actions

[Bill Deegan]

Does GH Actions allow caching files between runs? If so a MSVC cache file
would be a good candidate.
Though you'd need to invalidate it when newer MSVC's are installed in the
GHA's VM..


On Thu, May 1, 2025 at 9:53 AM Leonard de Ruijter <alderuijter at gmail.com>
wrote:

> Dear Joseph,
>
>
> Thanks for your extensive breakdown of the process.
>
> I have tried running cvarsall64.bat outside scons. Invocation of that
> takes approximately 5 seconds. I tried running vswhere earlier but without
> arguments, that's definitely smooth enough.
>
>
> Initializing an environment with tools=[] is fast, with tools=["msvc"] is
> slow. So we at least know for sure what tool is causing the delay.
>
>
> Regards,
>
>
> Leonard
> On 5/1/2025 4:20 PM, Joseph C. Brill wrote:
>
> There are a significant number of IO reads of the OS drive file system for
> MSVC batch file invocations and SCons MSVC initialization.
>
>
>
> In general, modern MSVC batch file invocations are “expensive”.
>
>
>
> It wouldn’t hurt to add the following to your build environment:
>
>     set VSCMD_SKIP_SENDTELEMETRY=1
>
>
>
> If nothing else, this may skip a powershell invocation to setup sending
> telemetry.
>
>
>
> After a brief look at the SConstructs in the SCons example, OSARA, and
> NVDA projects, I believe that the number of MSVC batch file invocations on
> an amd64 box for each is likely:
>
>    - 1: SCons example (0 default environments and 1 user environment)
>    - 2: OSARA (0 default environments and 2 user environments)
>    - 4: NVDA (1 default environment and 3 user environments)
>
>
>
> What follows is a high-level description of how MSVC is initialized.
> Errors are possible.  It may be easier to discuss in an SCons discussion.
>
>
>
> Simplified steps for MSVC initialization:
>
>    - Find the location of the vswhere executable
>    - Invoke vswhere
>    - For each version of MSVC detected:
>       - Check for the existence of a set of required compiler files
>    - For each Environment() unique combination of MSVC instance and
>    arguments:
>       - Call the MSVC batch file to configure environment
>
>
>
> Vswhere uses a “%ProgramData%” subdirectory  (OS drive) to load the COM
> server and possibly read data.
>
>
>
> Calling the 2022 MSVC batch file to configure the environment entails
> (local configuration):
>
>    - 17 or more batch file invocations
>    - 1 vswhere.exe invocation
>    - 0 or 1 powershell invocations to setup telemetry (
>    "%VSCMD_SKIP_SENDTELEMETRY%"=="")
>
>
>
> MSVC batch files may perform any of the following zero of more times:
>
>    - Check for the existence of directories and/or files
>    - Use the “where” command to search the system path
>    - Query the registry
>    - Change directories (cd/push/pop)
>    - File read
>
>
>
> The MSVC batch file skeleton call sequence below is for an amd64 box with
> HOST_ARCH=”amd64” and TARGET_ARCH=”amd64”.
>
>
>
> C:\Program Files\Microsoft Visual
> Studio\2022\Community\VC\Auxiliary\Build\vcvars64.bat:
>
> ·         "%~dp0vcvarsall.bat" x64 %*
>
> o "%~dp0..\..\..\Common7\Tools\vsdevcmd.bat"
>
> §  "%~dp0vsdevcmd\core\vsdevcmd_start.bat"
>
> ·         "%~dp0parse_cmd.bat" %*
>
> §  vswhere.exe
>
> §  "%VS170COMNTOOLS%VsDevCmd\core\dotnet.bat"
>
> ·         Reg queries
>
> §  "%VS170COMNTOOLS%VsDevCmd\core\msbuild.bat"
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%VsDevCmd\core\winsdk.bat"
>
> ·         Reg queries
>
> ·         Paths existence
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\ConnectionManagerExe.bat"
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\diaghub.bat"
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\html_help.bat"
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\netfxsdk.bat"
>
> ·         Reg queries
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\perf_tools.bat"
>
> ·         Reg queries
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\roslyn.bat"
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\team_explorer.bat"
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\testwindow.bat"
>
> ·         Path existence
>
> ·         Where
>
> §  "%VS170COMNTOOLS%vsdevcmd\ext\vcvars.bat"
>
> ·         Path existence
>
> ·         Dir contents
>
> ·         Where
>
> ·         File read
>
> §  if "%VSCMD_SKIP_SENDTELEMETRY%"==""
>
> ·         Powershell Send Telemetry
>
> §  "%~dp0vsdevcmd\core\vsdevcmd_end.bat"
>
> ·         Possible directory changes
>
>
>
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