CPU Tests: Microbenchmarks

Core-to-Core Latency

As the core count of modern CPUs is growing, we are reaching a time when the time to access each core from a different core is no longer a constant. Even before the advent of heterogeneous SoC designs, processors built on large rings or meshes can have different latencies to access the nearest core compared to the furthest core. This rings true especially in multi-socket server environments.

But modern CPUs, even desktop and consumer CPUs, can have variable access latency to get to another core. For example, in the first generation Threadripper CPUs, we had four chips on the package, each with 8 threads, and each with a different core-to-core latency depending on if it was on-die or off-die. This gets more complex with products like Lakefield, which has two different communication buses depending on which core is talking to which.

If you are a regular reader of AnandTech’s CPU reviews, you will recognize our Core-to-Core latency test. It’s a great way to show exactly how groups of cores are laid out on the silicon. This is a custom in-house test built by Andrei, and we know there are competing tests out there, but we feel ours is the most accurate to how quick an access between two cores can happen.

When we first reviewed the 10-core Comet Lake processors, we noticed that a core (or two) seemed to take slightly longer to ping/pong than the others. These two parts are both derived from the 10-core silicon but with two cores disabled, and we still see a pattern of some cores having additional latency. The ring on the 8-core parts still acts like a 10-core ring, but it all depends on which cores were disabled.

Frequency Ramping

Both AMD and Intel over the past few years have introduced features to their processors that speed up the time from when a CPU moves from idle into a high powered state. The effect of this means that users can get peak performance quicker, but the biggest knock-on effect for this is with battery life in mobile devices, especially if a system can turbo up quick and turbo down quick, ensuring that it stays in the lowest and most efficient power state for as long as possible.

Intel’s technology is called SpeedShift, although SpeedShift was not enabled until Skylake.

One of the issues though with this technology is that sometimes the adjustments in frequency can be so fast, software cannot detect them. If the frequency is changing on the order of microseconds, but your software is only probing frequency in milliseconds (or seconds), then quick changes will be missed. Not only that, as an observer probing the frequency, you could be affecting the actual turbo performance. When the CPU is changing frequency, it essentially has to pause all compute while it aligns the frequency rate of the whole core.

We wrote an extensive review analysis piece on this, called ‘Reaching for Turbo: Aligning Perception with AMD’s Frequency Metrics’, due to an issue where users were not observing the peak turbo speeds for AMD’s processors.

We got around the issue by making the frequency probing the workload causing the turbo. The software is able to detect frequency adjustments on a microsecond scale, so we can see how well a system can get to those boost frequencies. Our Frequency Ramp tool has already been in use in a number of reviews.

Both processors ramp from idle to full turbo in about six milliseconds, well within a single frame of standard gaming.

Power Consumption CPU Tests: Office and Science
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  • Samus - Friday, January 22, 2021 - link

    I don't think ANYONE actually wants to see the numbers for these chips at 65W :)
  • Spunjji - Monday, January 25, 2021 - link

    I love a good laugh!
  • iAPX - Saturday, January 23, 2021 - link

    I totally agree, a 5600X and a 10700 on their 65W TDP, and their maximum performance, to gives a baseline of what performance-level is WARRANTED by their makers.
  • etal2 - Thursday, January 21, 2021 - link

    Setting the limits in the bios is very nice and all but without the voltage regulation and thermal capacity they can not sustain this performance for very long regardless of the numbers set.

    I very much doubt that on the 60$ cheap 4 phase vrm boards the manufacturers set the limits very high, they will get fried boards within the warranty period and we know very well they can't have that.
  • Spunjji - Friday, January 22, 2021 - link

    That would be nice to see. Perhaps an article showing which of a representative selection of processors provide the best performance at a given set of fairly common power levels (65W / 95W / 125W).

    Something for when Dr Cutress finds himself with infinite time and no impending deadlines 😅
  • u.of.ipod - Thursday, January 21, 2021 - link

    So happy I waited patiently and got a Ryzen 5600x for my small form factor system. The fact it can hang with the i7's and only consumes 1/3 the peak power draw is great for heat output and playing nicely with SFX PSUs.
  • Golgatha777 - Thursday, January 21, 2021 - link

    And that's how you end up with graphs like this one.

  • Spunjji - Friday, January 22, 2021 - link

  • Samus - Friday, January 22, 2021 - link

  • magreen - Friday, January 22, 2021 - link

    Pentium 4 Extreme Edition all over again

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