Another look at HPET High Precision Event Timer

@kelzthetraxer

Note: I just updated the post above.

 

hello, I have got hpet disabled in bios but it still remains in device manager, is this expected behaviour? I tried uninstalling it and it reappeared again. I have seen a picture here previously of users computer without hpet on IRQ(0) only system timer, how did he achieved that?

 

I have no idea. I have never tried to disable it in Device Manager.

 

I have a small issue. After I delete useplatformclock, it tends to come come back for some reason. Anyone have idea why is that?

 

Deleting the value should make windows repopulate the setting with the default setting. Not totally get rid of it.

 

So how can I disable it permanently?

 

no, its totally gotten rid of. the bootloader's defaults are hard coded.

 

Just delete with bcdedit.exe until it disappears...

 

What's the difference between TSC Legacy, Default, and Enhanced?

 

We only know the context - the synchronization of TSCs across CPU cores.

 

bcdedit /deletevalue useplatformclock

 

It keeps coming back, so the only way is to disable instead of removing it.

 

No, it does not. I disabled HPET in BIOS and bcdedit /deletevalue useplatformclock gives 'no element found' which means HPET is disabled for good.

 

It does for me. It simply reappears on its own after few days.

 

"no element found" means that you removed the manually turned on/off setting from BCD configuration. It does not mean that HPET is disabled.

 

Maybe some software does that on your rig.

 

Maybe. But as I said, setting it to disabled keeps it off permanently.

 

Disabling in BIOS is a terrible idea, bcdedit /deletevalue useplatformclock is to set platformclock to factory settings, which means Windows will only use it if some programs need it or for stability in those programs, if not, Windows will not use it since it probably knows it's too slow for certain apps. But just forbidding Windows from using it out of pure paranoia or believeing you will get some latency benefits makes no sense at all.

Either way, when you install Windows, without any changes, bcdedit /deletevalue useplatformclock is the default value. Or automatic, which as I said, Windows will only use it on needed programs and it will "summon" it from your motherboard.

 

Your explanation is awkward a bit. "useplatformclock" is not about using HPET everywhere in Windows. It is about using any platform clock (timer, counter) as an implementation of two Win API functions - QueryPerformanceFrequency and QueryPerformaceCounter. When you force "useplatformclock yes" Windows looks for all available platform timers - timers outside the CPU (cores) - and chooses most appropriate for these two functions.
Any (enabled) platform clock can be used directly from OS kernel by any code.

PS When you force "useplatformclock no" only TSC - timer inside the CPU (cores) - will be used for QPF/QPC functions, but all (enabled) platform timers are still available to any OS kernel code.

 

I think it does. Because I've never removed it manually.