AMD and Intel Have Different HPET Guidance

A standard modern machine, with a default BIOS and a fresh Windows operating system, will sit on the first situation in the table listed above: the BIOS has HPET enabled, however it is not explicitly forced in the operating system. If a user sets up their machine with no overclocking or monitoring software, which is the majority case, then this is the implementation you would expect for a desktop.

AMD

We reached out to AMD and Intel about their guidance on HPET, because in the past it has both been unclear as well as it has been changed. We also reached out to motherboard manufacturers for their input.

For those that remember the Ryzen 7 1000-series launch, about a year ago from now, one point that was lightly mentioned among the media was that in AMD’s press decks, it was recommended that for best performance, HPET should be disabled in the BIOS. Specifically it was stated that:

Make sure the system has Windows High Precision Event Timer (HPET) disabled. HPET can often be disabled in the BIOS. [T]his can improve performance by 5-8%.

The reasons at the time were unclear as to why, but it was a minor part in the big story of the Zen launch so it was not discussed in detail. However, by the Ryzen 5 1000-series launch, that suggestion was no longer part of the reviewer guide. By the time we hit the Ryzen-2000 series launched last week, the option to adjust HPET in the BIOS was not even in the motherboards we were testing. We cycled back to AMD about this, and they gave the following:

The short of it is that we resolved the issues that caused a performance difference between on/off. Now that there is no need to disable HPET, there is no need for a toggle [in the BIOS].

Interestingly enough, with our ASUS X470 motherboard, we did eventually find the setting for HPET – it was not in any of the drop down menus, but it could be found using their rather nice ‘search’ function. I probed ASUS about whether the option was enabled in the BIOS by default, given that these options were not immediately visible, and was told:

It's enabled and never disabled, since the OS will ignore it by default. But if you enable it, then the OS will use it – it’s always enabled, that way if its needed it is there, as there would be no point in pulling it otherwise.

So from an AMD/ASUS perspective, the BIOS is now going to always be enabled, and it needs to be forced in the OS to be used, however the previous guidance about disabling it in the BIOS has now gone, as AMD expects performance parity.

It is worth noting that AMD’s tool, Ryzen Master, requires a system restart when the user first loads it up. This is because Ryzen Master, the overclocking and monitoring tool, requires HPET to be forced in order to do what it needs to do. In fact, back at the Ryzen 7 launch in 2017, we were told:

AMD Ryzen Master’s accurate measurements present require HPET. Therefore it is important to disable HPET if you already installed and used Ryzen Master prior to game benchmarking.

Ultimately if any AMD user has Ryzen Master installed and has been run at any point, HPET is enabled, even if the software is not running or uninstalled. The only way to stop it being forced in the OS is with a command to chance the value in the BCD, as noted above.

For the Ryzen 2000-series launch last week, Ryzen Master still requires HPET to be enabled to run as intended. So with the new guidance that HPET should have minimal effect on benchmarks, the previous guidance no longer applies.

Ryzen Master is not the only piece of software that requires HPET to be forced in order to do what it needs to do. For any of our readers that have used overclocking software and tools before, or even monitoring tools such as fan speed adjusters – if those tools have requested a restart before being used properly, there is a good chance that in that reboot the command has been run to enable HPET. Unfortunately it is not easy to generate a list, as commands and methods may change from version to version, but it can apply to CPU and GPU overclocking.

Intel

The response we had from Intel was a little cryptic:

[The engineers recommend that] as far as benchmarking is concerned, it should not matter whether or not HPET is enabled or not. There may be some applications that may not function as advertised if HPET is disabled, so to be safe, keep it enabled, across all platforms. Whatever you decide, be consistent across platforms.

A cold reading of this reply would seem to suggest that Intel is recommended HPET to be forced and enabled, however my gut told me that Intel might have confused ‘on’ in the BIOS with ‘forced’ through the OS, and I have asked them to confirm.

Looking back at our coverage of Intel platforms overall, HPET has not been mentioned to any sizeable degree. I had two emails back in 2013 from a single motherboard manufacturer stating that disabling HPET in the BIOS can minimise DPC latency on their motherboard, however no comment was made about general performance. I cannot find anything explicitly from Intel though.

A Timely Re-Discovery Forcing HPET On, Plus Spectre and Meltdown Patches
POST A COMMENT

242 Comments

View All Comments

  • Dr. Swag - Wednesday, April 25, 2018 - link

    It looks like you guys are re running all the benchmarks in the original review then, right? I see that the results look to be changed and less CPUs are on the lists (since you haven't rerun them all, I assume) Reply
  • Ryan Smith - Wednesday, April 25, 2018 - link

    Correct. We knew at the start of the Ryzen 2 review what benchmarks and what products we wanted to include; this timer issue hasn't changed that. Reply
  • freaqiedude - Wednesday, April 25, 2018 - link

    So would it be fair to say that Intel’s HPET implementation is potentially buggy? It seems to cause a disproportionate performance hit. Reply
  • chrcoluk - Wednesday, April 25, 2018 - link

    no its just that TSC + lapic is the way to go, There is a reason thats the default in windows and other modern OS's. Reply
  • DanNeely - Wednesday, April 25, 2018 - link

    It suggests that their implementation could probably be made less impactful than it currently is; but that high precision timers have had a performance impact has been known for a long time. In its guise as the multi-media timer in Windows over a decade ago the official MS docs recommended using lesser timing sources in lieu of it whenever possible because it would affect your system.

    What's new to the general tech site reading public is that there are apparently significant differences in the size of the impact between different CPU families.
    Reply
  • Tamz_msc - Wednesday, April 25, 2018 - link

    But is there a 'real' performance impact or does default HPET behavior simply introduce a fudge factor that alters how the tools report the numbers? Is there a way to verify the results externally? Reply
  • eddman - Wednesday, April 25, 2018 - link

    I'm wondering about the same thing. Do the games' frame rate really change (they get smoother or vice versa) or the timer just messes up the numbers reported by benchmarks and the games' actual frame rate that reaches the display doesn't change? Reply
  • rahvin - Wednesday, April 25, 2018 - link

    I'd be more concerned that Intel has found a way to make the timer report false benchmarks that are higher than they actually are. I'd also be curious if the graphics card/cpu combination is potentially at fault.

    Nvidia has been shown to cheat in the past on benchmarks by turning off features in certain games that are used for benchmarking to boost the score. Is Intel doing something similar?
    Reply
  • Rob_T - Wednesday, April 25, 2018 - link

    I came across a similar issue on VMware, where a virtual machine's clock would drift out of time synchronisation. The cause of this was that VMWare uses a software based clock and when a host was under heavy CPU load the VM's clock wouldn't get enough CPU resource to keep it updated accurately. This resulted in time running 'slowly' on the virtual machine.

    Under normal circumstances this kind of time driftissue would be handled by the Network Time Protocol daemon slewing the time back to accuracy; the problem is the maximum slew rate possible is limited to 500 parts-per-million (PPM). Under peak loads we were observing the VM's clock running slow by anywhere up to a third. This far outweighed the ability of the NTP slew mechanism to bring the time back to accuracy.

    If this issue has the same root cause, the software based timers would start to run slowly when the system is under heavy load. Therefore more work could be completed in a 'second' due to it's increased duration. It would be interesting to know if the highest discrepancy were also the ones with the largest CPU loads? Looking at the gaming graphs on page 4 the biggest differences are at 1080p which suggests this might be the case.
    Reply
  • oleyska - Wednesday, April 25, 2018 - link

    You also had Idle issue with windows servers where time would drift., the high load I've never heard of in our company we have thousands upon thousands of vm's using vmware though. Reply

Log in

Don't have an account? Sign up now