High Precision Event Timer....

[Erazor51]

I have an Asus P8Z77-V motherboard and in the bios there is a setting for High Precision Event Timer.

I noticed my DPC latency decreased when i disabled that feature but i have no idea what HPET is used for? is it safe to have it off?

Thanks

 

[BTRY B 529th FA BN]

It's safe either way.

IIRC it syncs up PCIe slots with a the os resolution timer er something along those lines.

I may have been way off. Here is a little more thorough explanation.

 

[mfenn]

It's very likely that your actual DPC latency didn't change much at all by disabling the HPET. What did change was the latency checker's access to a very fine grained clock source, thus making its measurements less accurate.

 

[Erazor51]

It's very likely that your actual DPC latency didn't change much at all by disabling the HPET. What did change was the latency checker's access to a very fine grained clock source, thus making its measurements less accurate.

I found the below searching on google and it looks like I get a more stable latency with it enabled in bios and in windows. By default it was just enabled in bios but disabled in windows.

By default Windows 7 uses different timers in the CPU to calculate stuff. HPET is the newest and best of these timers, but because of default combination of timers it takes longer time for CPU to keep up all the timers and sync between them. Forcing Windows to use HPET only improves performance and leads to greater FPS.

Steps to enable this tweak:

1. Enable HPET in BIOS. If you have HPET option in BIOS then your hardware can support HPET.

2. Enable HPET in Windows by giving this command in admin credential CMD:
bcdedit /set useplatformclock true

3. Reboot

Enabling HPET in BIOS is just half way of enabling HPET, it needs to be enabled in OS too, and in a way that it's the only timer used.

By default windows uses combination of TSC+ACPI timers, not matter if HPET is enabled in BIOS.

TSC+LAPICs Low performance (slow timers + syncing) = 2.76MHz
LAPICs low performance (slow timer - no syncing) = 3.5Mhz
TSC+HPET medium performance (slow and fast timer + syncing) = 3.8Mhz
HPET high performance (fast timer - no syncing) = 14.3MHz

Run the WinTimerTester 1.1 to see your QueryPerformanceFrequency
Then try with HPET, you'll be amazed.

HPET + platformclock=true will give you best timer resolution, frame rate and lowest DPC latency.

You can test timer ratio and QueryPerformanceFrequency with WinTimerTester 1.1 http://www.mediafire...xzo9n84d8lze9nb
The higher the QueryPerformanceFrequency is the better is performance. You only get high frequency with HPET. The other timers will give you significantly less frequency. Also note that if your ratio is not 1.0000 you are off set (or you have wrongly OC'ed), enable HPET and you should be without sync problems.

If you ever want to go back to default timers admin cmd:
bcdedit /deletevalue useplatformclock

Varying depending on setup, one should get increase up to +30 FPS and from the between.Online games is a good example of boost from HPET.