AMD Zen 2 Microarchitecture Analysis: Ryzen 3000 and EPYC Rome
by Dr. Ian Cutress on June 10, 2019 7:22 PM EST- Posted in
- CPUs
- AMD
- Ryzen
- EPYC
- Infinity Fabric
- PCIe 4.0
- Zen 2
- Rome
- Ryzen 3000
- Ryzen 3rd Gen
Editor's Note: With Zen 2 set to launch tomorrow (7/7), here's our architecture analysis from last month for some timely background information.
We have been teased with AMD’s next generation processor products for over a year. The new chiplet design has been heralded as a significant breakthrough in driving performance and scalability, especially as it becomes increasingly difficult to create large silicon with high frequencies on smaller and smaller process nodes. AMD is expected to deploy its chiplet paradigm across its processor line, through Ryzen and EPYC, with those chiplets each having eight next-generation Zen 2 cores. Today AMD went into more detail about the Zen 2 core, providing justification for the +15% clock-for-clock performance increase over the previous generation that the company presented at Computex last week.
AMD’s Zen 2 Product Portfolio
The current products that AMD has announced that have Zen 2 cores include the Ryzen 3rd Generation consumer CPUs, known as the Ryzen 3000 family, and AMD’s next generation enterprise EPYC processor, known as Rome. As of today, AMD has announced explicit details of six consumer Ryzen 3000 processors, including core counts, frequencies, memory support, and power. Details about the server processor, aside from some peak values, are expected in due course over the next few months.
| AMD 'Matisse' Ryzen 3000 Series CPUs | |||||||||||
| AnandTech | Cores Threads |
Base Freq |
Boost Freq |
L2 Cache |
L3 Cache |
PCIe 4.0 |
DDR4 | TDP | Price (SEP) |
||
| Ryzen 9 | 3950X | 16C | 32T | 3.5 | 4.7 | 8 MB | 64 MB | 16+4+4 | 3200 | 105W | $749 |
| Ryzen 9 | 3900X | 12C | 24T | 3.8 | 4.6 | 6 MB | 64 MB | 16+4+4 | 3200 | 105W | $499 |
| Ryzen 7 | 3800X | 8C | 16T | 3.9 | 4.5 | 4 MB | 32 MB | 16+4+4 | 3200 | 105W | $399 |
| Ryzen 7 | 3700X | 8C | 16T | 3.6 | 4.4 | 4 MB | 32 MB | 16+4+4 | 3200 | 65W | $329 |
| Ryzen 5 | 3600X | 6C | 12T | 3.8 | 4.4 | 3 MB | 32 MB | 16+4+4 | 3200 | 95W | $249 |
| Ryzen 5 | 3600 | 6C | 12T | 3.6 | 4.2 | 3 MB | 32 MB | 16+4+4 | 3200 | 65W | $199 |
The Zen 2 design paradigm, compared to the first generation of Zen, has changed significantly. The new platform and core implementation is designed around small 8-core chiplets built on TSMC’s 7nm manufacturing process, and measure around 74-80 square millimeters. On these chiplets are two groups of four-cores arranged in a ‘core complex’, or CCX, which contains those four cores and a set of L3 cache – the L3 cache is doubled for Zen 2 over Zen 1.
Each full CPU, regardless of how many chiplets it has, is paired with a central IO die through Infinity Fabric links. The IO die acts as the central hub for all off-chip communications, as it houses all the PCIe lanes for the processor, as well as memory channels, and Infinity Fabric links to other chiplets or other CPUs. The IO die for the EPYC Rome processors is built on Global Foundries' 14nm process, however the consumer processor IO dies (which are smaller and contain fewer features) are built on the Global Foundries 12nm process.
The consumer processors, known as ‘Matisse’ or Ryzen 3rd Gen or Ryzen 3000-series, will be offered with up to two chiplets for sixteen cores. AMD is launching six versions of Matisse on July 7th, from six cores to sixteen cores. The six and eight-core processors have one chiplet, while above this the parts will have two chiplets, but in all cases the IO die is the same. This means that every Zen 2 based Ryzen 3000 processor will have access to 24 PCIe 4.0 lanes and dual channel memory. Based on the announcements today, the prices will range from $199 for the Ryzen 5 3600, up to $700+ for the sixteen core (we’re waiting on final confirmation of this price).
The EPYC Rome processors, built on these Zen 2 chiplets, will have up to eight of them, enabling a platform that can support up to 64 cores. As with the consumer processors, no chiplet can communicate directly with each other – each chiplet will only connect directly to the central IO die. That IO die houses links for eight memory channels, and up to 128 lanes of PCIe 4.0 connectivity.
AMD’s Roadmap
Before diving into the new product line, it is worth recapping where we currently sit in AMD’s planned roadmap.
In previous roadmaps, showcasing AMD’s movement from Zen to Zen 2 and Zen 3, the company has explained that this multi-year structure will showcase Zen in 2017, Zen 2 in 2019, and Zen 3 by 2021. The cadence isn’t exactly a year, as it has depended on AMD’s design and manufacturing abilities, as well as agreements with its partners in the foundries and the current market forces.
AMD has stated that its plan for Zen 2 was to always launch on 7nm, which ended up being TSMC’s 7nm (Global Foundries wasn’t going to be ready in time for 7nm, and ultimately pulled the plug). The next generation Zen 3 is expected to align with an updated 7nm process, and at this point AMD has not made any comment about a potential ‘Zen 2+’ design in the works, although at this point we do not expect to see one.
Beyond Zen 3, AMD has already stated that Zen 4 and Zen 5 are currently in various levels of their respective design stages, although the company has not committed to particular time frames or process node technologies. AMD has stated in the past that the paradigms of these platforms and processor designs are being set 3-5 years in advance, and the company states it has to make big bets every generation to ensure it can remain competitive.
For a small insight into Zen 4, in an interview with Forrest Norrod, SVP of AMD’s Enterprise, Embedded, and Semi-Custom group, at Computex, he exclusively revealed to AnandTech the code name of AMD’s Zen 4 EPYC processor: Genoa.
| AMD EPYC CPU Codenames | |||
| Gen | Year | Name | Cores |
| 1st | 2017 | Naples | 32 x Zen 1 |
| 2nd | 2019 | Rome | 64 x Zen 2 |
| 3rd | 2020 | Milan | ? x Zen 3 |
| 4th | ? | Genoa | ? x Zen 4 |
| 5th | ? | ? | ? x Zen 5 |
Forrest explained that the Zen 5 code name follows a similar pattern, but would not comment on the time frame for the Zen 4 product. Given that the Zen 3 design is expected mid-2020, that would put a Zen 4 product for late 2021/early 2022, if AMD follows its cadence. How this will play into AMD’s consumer roadmap plans is unclear at this point, and will depend on how AMD approaches its chiplet paradigm and any future adjustments to its packaging technology in order to enable further performance improvements.
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Walkeer - Thursday, June 13, 2019 - link
Superb analysis, thanks a lot @Ian! very excited to have the 3900x at home alreadyFreckledTrout - Thursday, June 13, 2019 - link
Reading over the Zen2 microarchitecture article Im left wondering if the Windows scheduler improvements are making use of a new unmentioned RDPID feature in Zen2 to determine where threads are placed?cooker358 - Thursday, June 13, 2019 - link
感谢分享！Gastec - Thursday, June 13, 2019 - link
I too am curious about the latencies, particularly between the chiplets. With the clock selection down to 2 ns and Windows' 10 hopefully improved thread allocation (filling a CCX, then the next one before jumping to the 2nd chiplet) latencies should be lower. We'll just have to wait for honest extensive testing and reviews to be done. You were not planning on buying these CPUs on release day or even worse, pre-ordering them, were you? :)jamescox - Sunday, June 16, 2019 - link
I expect the CCX to CCX latencies to be very good. There is no memory clock on the cpu chiplet, so the two on die CCX almost certainly communicate at cpu clock rather than memory clock as in Zen 1. It isn’t the same as Intel’s mesh network, but AMD’s solution will have better L3 latency within the CCX compared to Intel. Intel’s mesh network seems to be terrible for power consumption. Intel’s ring bus didn’t scale to enough cores. For their 18 core chip (if I am remembering right), they actually had 3 separate ring buses. The mesh network is obviously not workable across multiple chiplets, so it will be interesting to see what Intel does.For the chiplet to chiplet latency, they have more than doubled the infinity fabric serdes clock with the higher than PCIe 4.0 speeds. It seems that the internal IF clock is also around doubled. It was operating at actual memory clock in Sen 1 which was half the DDR rate. They seem to be running the internal IF clock the same as the DDR rate with the option to drop back to half DDR rate. So if you are running DDR 3200, the IF clock may actually be 3200 instead of 1600 as it would be in Zen 1. If you re overclocking to DDR 4000 or something, then it may need to drop down to 2000 for the internal IF clock. If this is the way it is set up, then they may have an option to explicitly set the divider, but it is probably going to not be stable past 3.7 GHz or so. The IO die is 14 nm global foundries, so that seems like a reasonable limitation.
The CCX to CCX latency should be less important as the OS and software is better optimized for the architecture. There was quite a few cases on Zen 1 of applications performing significantly better on Linux compared to windows due to the scheduler. Most applications can be optimized a bit for this architecture also. The problem is fine grained shared memory between threads on different CCX. It generally a good idea to reduce that anyway since locking can be detrimental to performance. With Zen 2, I think application level optimizations are probably going to be a lot less necessary anyway, but a lot of the early issues were probably caused by bad multi-threaded programming. This type of architecture isn’t going away. Intel can’t compete with Epyc 2 with a monolithic die. Epyc 2 will be around 1000 square mm of silicon total. Intel can’t scale core count without moving to something similar.
frshi - Friday, June 14, 2019 - link
@Ian Cutress What about 2x16GB sticks compared to 4x8GB? I remember Zen and Zen+ were kinda picky when using 4 sticks. Any change to that on Zen 2?RAINFIRE - Saturday, June 15, 2019 - link
Yeah - I'm curious. Can anyone speak to the (4 x 32GB) memory that Ryzen 3000 and x570 boards are supposed to support?Holliday75 - Wednesday, June 19, 2019 - link
IF reviewers have samples at this time they are under an NDA until July 7th. Only unconfirmed leaks can provide that kind of info and its super early. A lot of these types of issues won't be known until they go retail.AdrianMel - Sunday, June 16, 2019 - link
I would like these AMD chips to be used on laptops. Would be a breakthrough in terms of computing power, lower consumption. I think if a HBM2 or higher memory is integrated into the processor, I think it will double the computing power. Ar fi de studiat si o implementare a 2 porturi superiare thnic vechiului expresscard 54 in care sa putem introduce in laptopuri 2 placi videojamescox - Sunday, June 16, 2019 - link
Everyone keeps bringing up HBM for cpus as if it is magical in some manner. HBM can provide high bandwidth, but it is still DRAM. He latency isn’t that great, so it isn’t really that useful as a cpu cache. If you are trying to run AVX512 code across a bunch of CPU cores, then maybe you could use the bandwidth. If you have code that can use that level of parallelism, then it will almost certainly run much more efficiently on an actual gpu. I didn’t think that expanding AVX to 512-bits was a good idea. There isn’t too much difference from a cpu perspective between 1 512-bit instruction and 2 256-bit instructions. The registers are wider, but they can have many more smaller registers that are specified in the ISA by using existing register renaming techniques. At 14 nm, the 512-bit units seem to take too much space and consume too much power. They may be more easily doable in 7 nm or below eventually, but they may still have issues running at cpu core clocks. If you have to run it at half clock (which is about where gpus are vs. cpus) then you have lost the advantage of going double the width anyway. IMO, the AVX 512 instructions were Intel’s failed attempt (Xeon Phi seems to have been a disappointment) at making a cpu act like a gpu. They have basically given that up and are now designing an actual gpu.I went off in a bit of a tangent there, but HBM really isn’t that useful for a cpu cache. It isn’t going to be that low of latency; so it would not increase single thread performance much compared to stuff actually designed to be a low latency cache. The next generations form AMD May start using active silicon interposers, but I would doubt that they would use HBM. The interposer is most likely to be used in place of the IO die. They could place all of the large transistors needed for driving off die interfaces (reason why IO doesn’t scale well) in the active interposer. They could then stack 7 nm chips on top of the active interposer for the actual logic. Cache scales very well which is why AMD can do a $200 chip with 32 MB of L3 cache and a $500 chip with 64 MB of L3. Intel 14 nm chips top out at 38.5 MB, mostly for high priced Xeon chips. With an active interposer, they could, for example) make something like 4 or 8 memory controller chips with large SRAM caches on 7 nm while using the active interposer for the IO drivers. Many different configurations are possible with an active interposer, so it is hard to speculate. Placing HBM on the IO interposer, as the AdoredTV guy has speculated, doesn’t sound like a great idea. Two stacks of HBM deliver 512 GB/s, which would take around 10 IF links to transfer to the CPU chiplets. That would be a massive waste of power. If they do use HBM for cpu chiplets, you would want to connect it directly to the cpu chiplet; you would place the a cpu chiplet and HBM stack on the same interposer. That would have some latency advantage, but mostly for large systems like Epyc.