PROCESSOR_POWER_INFORMATION.CurrentMhz no longer shows CurrentMhz about windows-dev-performance

[henrikand]

I work on Chrome and would also very much appreciate if the original support in Windows was restored to enable me to use user-mode (public and documented) APIs and track when throttling happens. There is support on macOS to track the CPU_Speed_Limit metric described in https://discussions.apple.com/thread/252039204 and it would be great if we could match this on Windows.

[randomascii]

This appears to have changed in build 21H1 (19043) because on my 20H2 (19042) machine CurrentMHz fluctuates according to load as it used to, but on my 21H1 machine it stays locked at the same value as MaxMhz.

[randomascii]

Update: the behavior in Windows 11 is the same as in build 19043. That is, the most recent version of Windows 10 and also Windows 11 never change the value returned for CurrentMhz, making detection of thermal throttling much more difficult.

[randomascii]

Further thoughts:

1. If CurrentMhz is no longer supported then the documentation should be updated to acknowledge this.
2. My reason for wanting CurrentMhz was so that I could compare it to the actual CPU frequency in order to detect thermal throttling. If this very useful technique (which I've used for 8+ years on several investigations) is no longer going to work then it becomes all the more important for the OS to expose this information (throttling status) in some other way. At the very least there needs to be some way to get it into ETW traces. Having it available from user mode would be better. Without throttling information (thermal or power) some types of performance problems become almost impossible to diagnose. That is, some mysterious performance problems are because the CPU is running at 800 MHz due to power or thermal constraints and unless information about the throttling is in ETW traces it is very hard to understand why things are running so slowly.

[ChrisOfTheLewi]

I saw this pop up in my email and while I can't comment on the originally reported problem, I did want to say that you can get the CPU frequency from ETW traces. I don't recall the specific provider off the top of my head (it's included with the CPU and GeneralProfile profiles running last I checked), but you can see it under CPU Frequencies in WPA (which shows up under Other and is documented here: https://docs.microsoft.com/en-us/windows-hardware/test/wpt/cpu-analysis ). I also find that information invaluable in tracking down performance issues fairly often. Hopefully this can help you out while waiting on a resolution to your reported problem.

[randomascii]

It sounds like CurrentMhz is not going to be coming back, due to changes in how the CPU and OS coordinate to choose CPU frequencies.

However the underlying issue of needing a way to detect thermal throttling remains. In order to focus on that underlying issue I filed a separate github issue at #101

This one can probably be closed.

[AvriMSFT]

Thanks Bruce for following up. I'll close this issue and add updates to #101