Conclusions: Not All Cores Are Made Equal

Designing a processor is often a finely tuned craft. To get performance, the architect needs to balance compute with throughput and at all times have sufficient data in place to feed the beast. If the beast is left idle, it sits there and consumes power, while not doing any work. Getting the right combination of resources is a complex task, and the reason why top CPU companies hire thousands of engineers to get it to work right. As long as the top of the design is in place, the rest should follow.

Sometimes, more esoteric products fall out of the stack. The new generation of AMD Ryzen Threadripper processors are just that – a little esoteric. The direct replacements for the previous generation units, replacing like for like but with better latency and more frequency, are a known component at this point and we get the expected uplift. It is just this extra enabled silicon in the 2990WX, without direct access to memory, is throwing a spanner in the works.

2950X (left) and 2990WX (right)

When some cores are directly connected to memory, such as the 2950X, all of the cores are considered equal enough that distributing a workload is a fairly easy task. With the new processors, we have the situation on the right, where only some cores are directly attached to memory, and others are not. In order to go from one of these cores to main memory, it requires an extra hop, which adds latency. When all the cores are requesting access, this causes congestion.

In order to take the full advantage of this setup, the workload has to be memory light. In workloads such as particle movement, ray-tracing, scene rendering, and decompression, having all 32-cores shine a light means that we set new records in these benchmarks.

In true Janus style, for other workloads that are historically scale with cores, such as physics, transcoding, and compression, the bi-modal core caused significant performance regression. Ultimately, there seems to be almost no middle ground here – either the workload scales well, or it sits towards the back of our high-end testing pack.

Part of the problem relates to how power is distributed with these big core designs. As shown on page four, the more chiplets that are in play, or the bigger the mesh, the more power gets diverted from the cores to the internal networking, such as the uncore or Infinity Fabric. Comparing the one IF link in the 2950X to the six links in 2990WX, we saw the IF consuming 60-73% of the chip power total at small workloads, and 25-40% at high levels.

In essence, at full load, a chip like the 2990WX is only using 60% of its power budget for CPU frequency. In our EPYC 7601, because of the additional memory links, the cores were only consuming 50% of the power budget at load. Rest assured, once AMD and Intel have finished fighting over cores, the next target on their list will be this interconnect.

But the knock on effect of not using all the power for the cores, as well as having a bi-modal operation of cores, is that some workloads will not scale: or in some cases regress.

The Big Cheese: AMD’s 32-Core Behemoth

There is no doubting that when the AMD Ryzen Threadripper 2990WX gets a change to work its legs, it will do so with gusto. We were able to overclock the system to 4.0 GHz on all cores by simply changing the BIOS settings, although AMD also supports features like Precision Boost Overdrive in Windows to get more out of the chip. That being said, the power consumption when using half of the cores at 4.0 GHz pushes up to 260W, leaving a full loaded CPU nudging 450-500W and spiking at over 600W. Users will need to make sure that their motherboard and power supply are up to the task.

This is the point where I mention if we would recommend AMD’s new launches. The 2950X slots right in to where the 1950X used to be, and at a lower price point, and we are very comfortable with that. However the 2950X already sits as a niche proposition for high performance – the 2990WX takes that ball and runs with it, making it a niche of a niche. To be honest, it doesn’t offer enough cases where performance excels as one would expect – it makes perfect sense for a narrow set of workloads where it toasts the competition. It even outperforms almost all the other processors in our compile test. However there is one processor that did beat it: the 2950X.

For most users, the 2950X is enough. For the select few, the 2990WX will be out of this world.

Thermal Comparisons and XFR2: Remember to Remove the CPU Cooler Plastic!
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  • ibnmadhi - Monday, August 13, 2018 - link

    It's over, Intel is finished. Reply
  • milkod2001 - Monday, August 13, 2018 - link

    Unfortunately not even close. Intel was dominating for last decade or so. Now when AMD is back in game, many will consider AMD but most will still get Intel instead. Damage was done.It took forever to AMD to recover from being useless and will take at least 5 years till it will get some serious market share. Better late than never though... Reply
  • tipoo - Monday, August 13, 2018 - link

    It's not imminent, but Intel sure seems set for a gradual decline. It's hard to eke out IPC wins these days so it'll be hard to shake AMD off per-core, they no longer have a massive process lead to lead on core count with their margins either, and ARM is also chipping away at the bottom.

    Intel will probably be a vampire that lives another hundred years, but it'll go from the 900lb gorilla to one on a decent diet.
    Reply
  • ACE76 - Monday, August 13, 2018 - link

    AMD retail sales are equal to Intel now...and they are starting to make a noticeable dent in the server market as well...it won't take 5 years for them to be on top...if Ryzen 2 delivers a 25% increase in performance, they will topple Intel in 2019/2020 Reply
  • HStewart - Monday, August 13, 2018 - link

    "AMD retail sales are equal to Intel now"

    Desktop maybe - but that is minimal market.
    Reply
  • monglerbongler - Monday, August 13, 2018 - link

    Pretty much this.

    No one really cares about workstation/prosumer/gaming PC market. Its almost certainly the smallest measurable segment of the industry.

    As far as these companies' business models are concerned:

    Data center/server/cluster > OEM consumer (dell, hp, microsoft, apple, asus, toshiba, etc.) > random categories like industrial or compact PCs used in hospitals and places like that > Workstation/prosumer/gaming

    AMD's entire strategy is to desperately push as hard as they can into the bulwark of Intel's cloud/server/data center dominance.

    Though, to be completely honest, for that segment they really only offer pure core count and PCIe as benefits. Sure they have lots of memory channels, but server/data center and cluster are already moving toward the future of storage/memory fusion (eg Optane), so that entire traditional design may start to change radically soon.

    All important: Performance per unit of area inside of a box, and performance per watt? Not the greatest.

    That is exceptionally important for small companies that buy cooling from the power grid (air conditioning). If you are a big company in Washington and buy your cooling via river water, you might have to invest in upgrades to your cooling system.

    Beyond all that the Epyc chips are so freaking massive that they can literally restrict the ability to design 2 slot server configuration motherboards that also have to house additional compute hardware (eg GPGPU or FPGA boards). I laugh at the prospect of a 4 slot epyc motherboard. The thing will be the size of a goddamn desk. Literally a "desktop" sized motherboard.

    If you cant figure it out, its obvious:

    Everything except for the last category involves massive years-spanning contracts for massive orders of hundreds of thousands or millions of individual components.

    You can't bet hundreds of millions or billions in R&D, plus the years-spanning billion dollar contracts with Global Foundries (AMD) or the tooling required to upgrade and maintain equipment (Intel) on the vagaries of consumers, small businesses that make workstations to order, that small fraction of people who buy workstations from OEMs, etc.

    Even if you go to a place like Pixar studios or a game developer, most of the actual physical computers inside are regular, bone standard, consumer-level hardware PCs, not workstation level equipment. There certainly ARE workstations, but they are a minority of the capital equipment inside such places.

    Ultimately that is why, despite all the press, despite sending out expensive test samples to Anandtech, despite flashy powerpoint presentations given by arbitrary VPs of engineering or CEOs, all of the workstation/Prosumer/gaming stuff is just low-binned server equipment.

    because those are really the only 2 categories of products they make;

    pure consumer, pure workstation. Everything else is just partially enabled/disabled variations on those 2 flavors.
    Reply
  • Icehawk - Monday, August 13, 2018 - link

    I was looking at some new boxes for work and our main vendors offer little if anything AMD either for server roles or desktop. Even if they did it's an uphill battle to push a "2nd tier" vendor (AMD is not but are perceived that way by some) to management. Reply
  • PixyMisa - Tuesday, August 14, 2018 - link

    There aren't any 4-socket EPYC servers because the interconnect only allows for two sockets. The fact that it might be difficult to build such servers is irrelevant because it's impossible. Reply
  • leexgx - Thursday, August 16, 2018 - link

    is more then 2 sockets needed when you have so many cores to play with Reply
  • Relic74 - Wednesday, August 29, 2018 - link

    Actually there are, kind of, supermicro for example has created a 4 node server for the Epyc. Basically it's 4 computers in one server case but the performance is equal to that if not better than that of a hardware 4 socket server. Cool stuff, you should check it out. In fact, I think this is the way of the future and multi socket systems are on their way out as this solution provides more control over what CPU. As well as what the individual cores are doing and provides better power management as you can shut down individual nodes or put them in stand by where as server with 4 sockets/CPU's is basically always on.

    There is a really great white paper on the subject that came out of AMD, where the stated that they looked into creating a 4 socket CPU and motherboard capable of handling all of the PCI lanes needed, however it didn't make any sense for them to do so as there weren't any performance gains over the node solution.

    In fact I believe we will see a resurrection of blade systems using AMD CPU's, especially now with all of the improvements that have been made with multi node cluster computing over the last few years.
    Reply

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