PCIe 4.0

As the first commerical x86 server CPU supporting PCIe 4.0, the I/O capabilities of second generation EPYC servers are top of the class. One PCIe 4.0 x16 offers up to 32 GB/s in both direction, so each socket offers up to 256 GB/s in both directions, for a full 128 PCIe 4.0 lanes per CPU. 

Each CPU has 8 x16 PCIe 4.0  links available which can be split up among up to 8 devices per PCIe root, as shown above. There is also full PCIe peer-to-peer support both within a single socket and across sockets.

With the previous generation, in order to enable a dual socket configuration, 64 PCIe lanes from each CPU were used to link them together. For EPYC, AMD still allows for 64 PCIe lanes to be used, but these are PCIe 4.0 lanes now. There is also another feature that AMD has here - socket-to-socket IF link bandwidth management - which allows OEM partners to design dual-socket systems with less socket-to-socket bandwidth and more PCIe lanes if needed. 

We also learned that there are in fact 129 PCIe 4.0 lanes on each CPU. On each CPU there is one extra PCIe lane for the BMC (the chip that controls the server). Considering we are living in the age of AI acceleration, the EPYC 7002 servers will be great as hosts for quite a few GPUs or TPUs. Density has never looked so fun.

Zen 2 and Rome: SMILE For Performance The BIG LIST of Rome CPUs: Core Counts and Frequencies
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  • schujj07 - Friday, August 9, 2019 - link

    The problem is Microsoft went to the Oracle model of licensing for Server 2016/19. That means that you have to license EVERY CPU core it can be run on. Even if you create a VM with only 8 cores, those 8 cores won't always be running on the same cores of the CPU. That is where Rome hurts the pockets of people. You would pay $10k/instance of Server Standard on a single dual 64 core host or $65k/host for Server DataCenter on a dual 64 core host.
  • browned - Saturday, August 10, 2019 - link

    We are currently a small MS shop, VMWare with 8 sockets licensed, Windows Datacenter License. 4 Hosts, 2 x 8 core due to Windows Licensing limits. But we are running 120+ majority Windows systems on those hosts.

    I see our future with 4 x 16 core systems, unless our CPU requirements grow, in which case we could look at 3 x 48 or 2 x 64 core or 4 x 24 core and buy another lot of datacenter licenses. Because we already have 64 cores licensed the uplift to 96 or 128 is not something we would worry about.

    We would also get a benefit from only using 2, 3, or 4 of our 8 VMWare socket licenses. We could them implement a better DR system, or use those licenses at another site that currently use Robo licenses.
  • jgraham11 - Thursday, August 8, 2019 - link

    so how does it work with hyper threaded CPUs? And what if the server owner decides to not run Intel Hyperthreading because it is so prone to CPU exploits (most 10 yrs+ old). Does Google still pay for those cores??
  • ianisiam - Thursday, August 8, 2019 - link

    You only pay for physical cores, not logical.
  • twotwotwo - Thursday, August 8, 2019 - link

    Sort of a fun thing there is that in the past you've had to buy more cores than you need sometimes: lower-end parts that had enough CPU oomph may not support all the RAM or I/O you want, or maybe some feature you wanted was absent or disabled. These seem to let you load up on RAM and I/O at even 8C or 16C (min. 1P or 2P configs).

    Of course, some CPU-bound apps can't take advantage of that, but in the right situation being able to build as lopsided a machine as you want might even help out the folks who pay by the core.
  • azfacea - Wednesday, August 7, 2019 - link

  • NikosD - Wednesday, August 7, 2019 - link

    Ok guys...The Anandtech's team had a "bad luck and timming issues" to offer a true and decent review of the Greatest x86 CPU of all time, so for a proper review of EPYC Rome coming from the most objective and capable site for servers, take a look here:
  • anactoraaron - Thursday, August 8, 2019 - link

  • phoenix_rizzen - Saturday, August 10, 2019 - link

    Review article for new CPU devolves into Windows vs Linux pissing match, completely obscuring any interesting discussion about said hardware. We really haven't reached peak stupid on the internet yet. :(
  • The Benjamins - Wednesday, August 7, 2019 - link

    Can we get a C20 benchmark for the lulz?

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