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
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  • Lord of the Bored - Thursday, April 26, 2018 - link

    Not just nVidia. AMD's graphics division has been known to do it too, going back to when it was still an independent company. See: QUAFF3.EXE Reply
  • Maxiking - Saturday, April 28, 2018 - link

    Yeah like AMD was using less demanding tessellation to boost their score in benchmarks or less demanding AF ignoring completely what an application set. . Oh yeah, I forgot, when the same thing happened to AMD, it was a bug, when to Nvidia, cheating. Those double standards are hilarious. Reply
  • Fallen Kell - Wednesday, April 25, 2018 - link

    The overhead of HPET causes the Intel CPUs to effectively slow down with the combination of the Meltdown+Spectre fixes. HPET is a system call which results in the harshest penalty of the fixes for Meltdown+Spectre. Add to the fact that Intel's implementation of HPET is higher fidelity (i.e. higher speed clock rate) than the specification requires, and then combine that higher fidelity with creating an even larger load on the CPU (due to Meltdown+Spectre), and it creates the large performance degradation.

    The other timers (TSC + lapic) do not incur as high a penalty, as these do not result in system calls which need to be protected from Meltdown/Spectre exploitation.
    Reply
  • mczak - Wednesday, April 25, 2018 - link

    The higher clock the HPET runs at for intel should make absolutely no difference - it's the cost of reading the timer which counts, the rate it's running at should not be relevant. (Although I higher frequency may have higher hw implementation cost.).
    For this kind of slowdown as shown in some games though there have to be LOTS of timer queries. But I suppose it's definitely possible (I suspect nowadays everyone uses the TSC based queries and forget to test without them being available), which are much faster in hw and don't require syscalls. Meltdown (and probably to a lesser degree Spectre) could indeed have a big impact on performance with HPET (if there's that many timing queries). I'd like to see some data with HPET but without these patches.
    Reply
  • looncraz - Wednesday, April 25, 2018 - link

    I believe, from my own testing, that it's merely a factor of reporting. HPET has always resulted in a smoother, faster, system with less stutters when I enable it.

    I also use SetTimerResolutionService to great effect.
    Reply
  • tamalero - Thursday, April 26, 2018 - link

    Its interesting how it is very different from person to person.

    I usually had HPET on with my intel Quadcores..

    But once I got my Threadripper I had to disable and remove HPET. If not I would get horrible stuttering.
    Reply
  • GreenReaper - Friday, April 27, 2018 - link

    It may be more *responsive*, yet able to do less work. In fact, speed and latency can be opposites - if you never pick your head up while doing a task, you'll probably execute it in the fastest possible time, at the expense of anything else that you might have wanted to do during that time. Most interactive users don't appreciate the computer not paying attention to them, so desktop computers tradeoff for speed for reduced latency - although with multi-core systems the impact is small.

    In the past when the TSC was not present, HPET also moved the system more towards being a real-time system, and the cost of that the overhead of the more frequent timer checks. Nowadays, especially with nonstop TSC (not impacted by power management), I'm not sure that is the case, but using it might still change latency - for good or ill.

    Enabling HPET does not mandate forcing its use over the alternatives, but mandating it with 'bcdedit /set useplatformclock true' does. You can do the equivalent on Linux. And clearly, there is a cost, although that cost varies greatly depending on the platform and what you are doing.

    Over the years I've seen numerous cases of people trying to reduce the number of gettimeofday calls to increase performance, and the cost of checking the HPET is probably one of the reasons.
    Reply
  • Ryan Smith - Thursday, April 26, 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?"

    Yes, you can compare the clocks with various applications, including the Timers applications. Which in our case shows that neither the ACPI nor QPC timers are drifting versus the HPET timer. So the performance difference really is a performance difference, and not a loss of timer accuracy.

    https://images.anandtech.com/doci/12678/TimerBench...
    Reply
  • chrcoluk - Wednesday, April 25, 2018 - link

    Disabling TSC is a big nono.

    Forced HPET as an example will disable optimised interrupts for network cards, the AMD and intel review support staff probably dont have the knowledge to correctly advise you. I suggest you contact microsoft.

    Also your cpu's tested, what decides what cpu's you decided to compare to? the AMD review guide or something else? Was a lot of omitted CPU's and noticeably no manual overclocked intel cpu's in your data.

    See my first reply, if AMD software is forcing HPET and especially if they not informing the user the consequences of doing this then thats very irresponsible.
    Reply
  • eddman - Thursday, April 26, 2018 - link

    Some rather interesting info on timers from MS: https://msdn.microsoft.com/en-us/library/windows/d... Reply

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