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
Comments Locked


View All Comments

  • Cooe - Thursday, August 8, 2019 - link

    Hexus got around ≈31,000 iirc.
  • Ryan Smith - Thursday, August 8, 2019 - link

    Funny enough, from what I've heard from other people who have tested it, it actually doesn't run all that well with dual EPYCs. Too many cores that are too fast, to the point that initialization times are starting to hold back performance.
  • Ian Cutress - Thursday, August 8, 2019 - link

    I got a message from the Cinebench team at one point. They don't spawn/kill/respawn for each little segment: it's kept alive and just fed more data. CB20 is also designed to scale, given that CB15 freaked out above 32 cores or so
  • prisonerX - Wednesday, August 7, 2019 - link

    Where is our resident Intel shill? Selling his INTC stock in a panic perhaps?
  • abufrejoval - Wednesday, August 7, 2019 - link

    comiserating with the ARM server guys
  • Lord of the Bored - Thursday, August 8, 2019 - link

    Not gonna lie, I scrolled straight to the comments to see the Intel fanboy spinning this. Instead I got a wall of... Call of Duty references, I think?
  • PeachNCream - Friday, August 9, 2019 - link

    The fact that AMD released a product that breaks even HStewart's ability to defend shill for Intel should say something pretty epic about Epyc.
  • Lord of the Bored - Saturday, August 10, 2019 - link

    You ain't lyin' there. Seems the name was chosen well.
  • Korguz - Saturday, August 10, 2019 - link

    i bet, he would STILL but the intel cpu too. even though it costs more, slower and probably uses more power.
  • Samus - Thursday, August 8, 2019 - link

    I was just thinking if Trump doesn't crash the market with his shenanigans then AMD could be an incredibly good buy in the next few months. The first time they've been a good buy in awhile.

    Although a lot of my daytrader friends have always claimed AMD was a good short-term buy, which is partially true, but if they can keep momentum and Intel doesn't try strongarming them out of OEMs (you know, like they used too...)

Log in

Don't have an account? Sign up now