Core-to-Core, Cache Latency, Ramp

For some of our standard tests, we look at how the CPU performs in a series of synthetic workloads to example any microarchitectural changes or differences. This includes our core-to-core latency test, a cache latency sweep across the memory space, and a ramp test to see how quick a system runs from idle to load.


Inside the chip are eight cores connected through a bi-directional ring, each direction capable of transmitting 32 bytes per cycle. In this test we test how long it takes to probe an L3 cache line from a different core on the chip and return the result.

For two threads on the same core, we’re seeing a 7 nanosecond difference, whereas for two separate cores we’re seeing a latency from 15.5 nanoseconds up to 21.2 nanoseconds, which is a wide gap. Finding out exactly how much each jump takes is a bit tricky, as the overall time is reliant on the frequency of the core, of the cache, and of the fabric over the time of the test. It also doesn’t tell us if there is anything else on the ring aside from the cores, as there is also going to be some form of external connectivity to other elements of the SoC.

However, compared to the Zen3 numbers we saw on the Ryzen 9 5980HS, they are practically the same.

Cache Latency Ramp

This test showcases the access latency at all the points in the cache hierarchy for a single core. We start at 2 KiB, and probe the latency all the way through to 256 MB, which for most CPUs sits inside the DRAM.

Part of this test helps us understand the range of latencies for accessing a given level of cache, but also the transition between the cache levels gives insight into how different parts of the cache microarchitecture work, such as TLBs. As CPU microarchitects look at interesting and novel ways to design caches upon caches inside caches, this basic test proves to be very valuable.

The data here again mirrors exactly what we saw with the previous generation on Zen3.

Frequency Ramp

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.

A ramp time of within one millisecond is as expected for modern AMD platforms, although we didn’t see the high 4.9 GHz that AMD has listed this processor as being able to obtain. We saw it hit that frequency in a number of tests, but not this one. AMD’s previous generation took a couple of milliseconds to hit around the 4.0 GHz mark, but then another 16 milliseconds to go full speed. We didn’t see it in this test, perhaps due to some of the new measurements AMD is doing on core workload and power. We will have to try this on a different AMD Ryzen 6000 Mobile system to see if we get the same result.

AMD's Ryzen 9 6900HS Rembrandt Benchmarked Power Consumption
Comments Locked


View All Comments

  • mode_13h - Tuesday, March 1, 2022 - link

    > 3D Particle Movement v2.1
    > ...
    > To keep things honest, AMD also has a copy of the code, but has not proposed any changes.

    No, to keep things honest, you need to release the benchmark. All of your other benchmarks are publicly-available, but not this one.

    Please open source it, or stop using it. Thanks.
  • isthisavailable - Wednesday, March 2, 2022 - link

    So there are no battery life and iGPU results in a mobile processor review...right.
  • mode_13h - Wednesday, March 2, 2022 - link

    IMO, the article was long enough and had plenty to cover. I think it's not a problem, if those are reviewed separately, however it does make the overall comparison vs. Intel problematic.

    Anyway, we now know Ian was writing it on his way out the door, so that makes it at least understandable.
  • Stuka87 - Wednesday, March 2, 2022 - link

    I am awaiting the day where Ryzens become more widespread in workstation class laptops. Very few machines had them when I had to upgrade this past summer, so had to go Intel. Which has been a bit lack luster.
  • PlanetLockdownFilm - Wednesday, March 2, 2022 - link

    Interesting read, buts seems like it depends on what offer you can find and what else the laptop has to give. RDNA2 is a plus though, if you're going for integrated graphics.
  • WaltC - Wednesday, March 2, 2022 - link

    I thought it was fairly interesting that although I looked for it, I could not find a description of the system used to supply the Intel numbers that were plugged into the charts used--if those specs are included and I missed them, then mea culpa. But if not, well, that's interesting...and I also found it very interesting that Intel was nowhere to be found/mentioned in the Performance Per Watt section...;)
  • mode_13h - Thursday, March 3, 2022 - link

    > I also found it very interesting that Intel was nowhere to be found/mentioned
    > in the Performance Per Watt section...;)

    Exactly. What they did show was that Intel could/would scale up power consumption of its single-core performance higher than Zen 3+. What's not obvious is how much of Intel's performance advantage simply comes down to juicing their P-cores, at the expense of efficiency.
  • Dug - Friday, March 11, 2022 - link

    I want to see how well each system does when not plugged in.
  • m16 - Thursday, March 3, 2022 - link

    Wow, I know what I'll be recommending for non desktop replacements.

    This specific laptop also perhaps helps a bit, that's how I'd expect other manufacturers to build their workhorses for decent cooling.
  • beginner99 - Friday, March 4, 2022 - link

    Now AT isn't doing GPU tests on an APU. I mean really?

Log in

Don't have an account? Sign up now