Last week, we published our AMD 2nd Gen Ryzen Deep Dive, covering our testing and analysis of the latest generation of processors to come out from AMD. Highlights of the new products included better cache latencies, faster memory support, an increase in IPC, an overall performance gain over the first generation products, new power management methods for turbo frequencies, and very competitive pricing.

In our review, we had a change in some of the testing. The big differences in our testing for this review was two-fold: the jump from Windows 10 Pro RS2 to Windows 10 Pro RS3, and the inclusion of the Spectre and Meltdown patches to mitigate the potential security issues. These patches are still being rolled out by motherboard manufacturers, with the latest platforms being first in that queue. For our review, we tested the new processors with the latest OS updates and microcode updates, as well as re-testing the Intel Coffee Lake processors as well. Due to time restrictions, the older Ryzen 1000-series results were used.

Due to the tight deadline of our testing and results, we pushed both our CPU and gaming tests live without as much formal analysis as we typically like to do. All the parts were competitive, however it quickly became clear that some of our results were not aligned with those from other media. Initially we were under the impression that this was as a result of the Spectre and Meltdown (or Smeltdown) updates, as we were one of the few media outlets to go back and perform retesting under the new standard.

Nonetheless, we decided to take an extensive internal audit of our testing to ensure that our results were accurate and completely reproducible. Or, failing that, understanding why our results differed. No stone was left un-turned: hardware, software, firmware, tweaks, and code. As a result of that process we believe we have found the reason for our testing being so different from the results of others, and interestingly it opened a sizable can of worms we were not expecting.

An extract from our Power testing script

What our testing identified is that the source of the issue is actually down to timers. Windows uses timers for many things, such as synchronization or ensuring linearity, and there are sets of software relating to monitoring and overclocking that require the timer with the most granularity - specifically they often require the High Precision Event Timer (HPET). HPET is very important, especially when it comes to determining if 'one second' of PC time is the equivalent to 'one second' of real-world time - the way that Windows 8 and Windows 10 implements their timing strategy, compared to Windows 7, means that in rare circumstances the system time can be liable to clock shift over time. This is often highly dependent on how the motherboard manufacturer implements certain settings. HPET is a motherboard-level timer that, as the name implies, offers a very high level of timer precision beyond what other PC timers can provide, and can mitigate this issue. This timer has been shipping in PCs for over a decade, and under normal circumstances it should not be anything but a boon to Windows.

However, it sadly appears that reality diverges from theory – sometimes extensively so – and that our CPU benchmarks for the Ryzen 2000-series review were caught in the middle. Instead of being a benefit to testing, what our investigation found is that when HPET is forced as the sole system timer, it can  sometimes a hindrance to system performance, particularly gaming performance. Worse, because HPET is implemented differently on different platforms, the actual impact of enabling it isn't even consistent across vendors. Meaning that the effects of using HPET can vary from system to system, as well as the implementation.

And that brings us to the state HPET, our Ryzen 2000-series review, and CPU benchmarking in general. As we'll cover in the next few pages, HPET plays a very necessary and often very beneficial role in system timer accuracy; a role important enough that it's not desirable to completely disable HPET – and indeed in many systems this isn't even possible – all the while certain classes of software such as overclocking & monitoring software may even require it. However for a few different reasons it can also be a drain on system performance, and as a result HPET shouldn't always be used. So let's dive into the subject of hardware timers, precision, Smeltdown, and how it all came together to make a perfect storm of volatility for our Ryzen 2000-series review.

A Timely Re-Discovery
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  • ReverendCatch - Wednesday, April 25, 2018 - link

    I feel like what this ultimately means is Intel has issues with HPET, and that the results everyone else are getting are the problematic ones, not you guys. By forcing a more precise timer, intel's... I dunno... "advantage" as it were is eliminated.

    Seriously, AMD is 1% or less variance despite the timer used. Intel is upward of 30% or more. To me, that is a giant red flag.
  • nevcairiel - Wednesday, April 25, 2018 - link

    Except that normal systems are not going to force HPET, so the more real-world realistic tests/results should really be used.
  • ReverendCatch - Wednesday, April 25, 2018 - link

    The question I suppose I have is, are the results even real or legit at that point. Why does the intel suffer tremendously when using an accurate timer, and pulls ahead when not?

    How does that not sound fishy to you?
  • tmediaphotography - Wednesday, April 25, 2018 - link

    From my reading of the article, it seems that Intel takes a larger hit because they use a more accurate HPET timer (24Mhz on the 8700K), and thus it is more taxing on the system. The calls are very much under the umbrella of things more negatively affected by Spectre, and as the i7 8700K system had an HPET rate at closing on 2x as much as the R7 2700K, it stands to reason the i7 is going to benefit much more from it being turned off.

    tl;dr, the more accurate timer is much more needy on the system, and the system under spectre/meltdown takes an even larger hit at the IO calls to it.
  • Billy Tallis - Wednesday, April 25, 2018 - link

    The HPET can run at a higher frequency without generating more CPU overhead, because it's really just a counter. Making that counter's value grow more quickly doesn't mean the CPU gets more interrupts per second.
  • patrickjp93 - Wednesday, April 25, 2018 - link

    Because it makes perfect sense. Intel's losing more clock cycles since it is at vastly higher clock speeds, and it has Meltdown to contend with on top of Spectre. HPET from my cursory reading is 4 system calls compared to just 2 for TSC+lapic. The performance hit of that should then surprise no one.

    With AVX-512, Intel has a lot of very high throughput instructions that AMD doesn't. If your software uses them, Intel pulls ahead vs. the best equivalent you could write for Epyc. That's not fishy. You're just taking the more optimal path to solving your problem. When Cascade Lake X and Cannon/Ice Lake arrive, this will all be fixed at the hardware level and the overhead will disappear.
  • Cooe - Wednesday, April 25, 2018 - link

    Except that isn't actually true in practice for a wide variety of actual AVX-512 enabled workloads. Running those insanely wide registers drastically increases power draw & thermal ouput and as a result clock-speeds take a nose-dive. In certain SIMD workloads capable of AVX acceleration, this clock-dropoff is so large that EPYC outperforms Skylake-X's AVX-512 support using much much narrower AVX2 instructions/registers simply because it can maintain vastly higher clock-speeds during the load.

    Heck AnandTech even verified this with their own testing way back when.
  • patrickjp93 - Wednesday, April 25, 2018 - link

    If you're using the widest registers, yes, but there were also a lot of 128 and 256-bit extensions added that were missing from the AVX/2 stack. And Intel will bring the power draw down and the clocks up over time.
  • Dolda2000 - Wednesday, April 25, 2018 - link

    The HPET, despite its name, is not more accurate. The TSC timer is accurate to CPU clock-cycle precision, which is usually more than two orders of magnitude better than the HPET.
  • Billy Tallis - Wednesday, April 25, 2018 - link

    The difference between accuracy and precision is probably important here. TSC is definitely far more precise, but overclocking can make it much less accurate.

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