[Scons-users] SCons very slow on GitHub actions

[Joseph C. Brill]

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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