[Scons-users] SCons very slow on GitHub actions

[Leonard de Ruijter]

I just discovered the environment variable SCONS_MSCOMMON_DEBUG.

You can download the log here: 
https://github.com/LeonarddeR/scons-examples/actions/runs/14780113619/artifacts/3045818756

There is not much interesting info in it, apart from that it seems yet 
to be the vcvars64.bat call that takes so long.

That raises the question, why is that invocation only needing around 5 
seconds when running in cmd, whereas it takes much longer within scons 
itself? Is it possibly writing stuff to the file system under the hood?


Regards,


Leonard

On 5/1/2025 6:53 PM, Leonard de Ruijter 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:
>>       o Check for the existence of a set of required compiler files
>>   * For each Environment() unique combination of MSVC instance and
>>     arguments:
>>       o 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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