IIS worker process profiling fails with "Unexpected error" message

[markashleybell]

I'm not sure whether this is totally outside the scope of this project or not, and I'm not clear whether it's intended for working with .NET Framework code or just .NET Core... so if I'm just using it wrong, please feel free to close this!

My use case would be attaching to a running IIS worker process (w3wp.exe) to profile a web application. However, when I try that by attaching to the PID, I get the following error:

Unexpected error: The requested resource is in use. (0x800700AA)

Is this a bug, or am I doing something wrong (or is Ultra just not really intended for profiling web apps)?

[xoofx]

Is this a bug, or am I doing something wrong (or is Ultra just not really intended for profiling web apps)?

I don't think it is a bug with ultra but something else with ETW/Windows that would happen if you were using another ETW based profiler. Others have been experiencing this similar issue:

• COMException when generating ETW Log for benchmark dotnet/BenchmarkDotNet#2139
• I got a lot of .etl.zip files that have zeroes in CPU Msec for every process. CPU Stack is empty, but Thread Time Stack show correct information microsoft/perfview#1726
• COMException occuring when kernel events are collected microsoft/perfview#1723

You could try the workaround described here and see if it solves your issue.

[markashleybell]

Yep, I can confirm that running the following in my elevated Powershell terminal allowed me to profile successfully:

Set-MpPreference -DisableTDTFeature $true

And ultra works really well! Looking forward to having a proper play with this tomorrow.

Incidentally (for anyone who stumbles across this), you can also re-enable the disabled feature easily enough after a profiling session:

# Re-enable TDT
Set-MpPreference -DisableTDTFeature $false

# Check the current status
Get-MpPreference | Select-Object -ExpandProperty IntelTDTEnabled