Server Processors

[iamdady]

Hi all,

   We have test a AMD EPYC 7451 server, and some thine weird comes up:

The topology of 7451 is created by lstopo Linux command in the attachment file, what's confusing me is why PU P40, PU P88, PU P2, PU P50 share a same L3 Cache(see bellow) but in two different NUMANode? Different NUMANode means different die, that's impossible for one L3 cache cross two die.

The L3 share information is obtained from bellow command:

$ cat cpu40/cache/index3/shared_cpu_list

2,40,50,88

Thanks a lot!

[Anonymous]

Hi iamdady,

That is strange. Would you do me a favor and provide the following:

• Vendor
• BIOS
• OS and version
• Kernel version if not default
• Dump of lscpu command to a file as well

[iamdady]

Hi,

Sorry for the account name, my name is Heron.

Vendor: Dell

BIOS: version 1.1.3

OS: No LSB modules are available.

Distributor ID: Ubuntu

Description: Ubuntu 16.04.4 LTS

Release: 16.04

Codename: xenial

Kernel: Linux 4.4.0-119-generic #143-Ubuntu SMP Mon Apr 2 16:08:24 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Lscpu: see attached file

Other info may help:

System Model: Name

PowerEdge R7425

UEFI Compliance Version

2.5

Thanks a lot!

[abucodonosor]

This indeed looks weird .. However I don't think 4.4.* kernels have all AMD topology fixes.

Is possble for you to try an newer kernel ?

[iamdady]

Hi,

I upgrade the Kernel to 4.16.2 and the topology changed as you think, see the attached file, so is this right now?

[abucodonosor]

Can you please just post output of lscpu ?

[iamdady]

Thank you very much.

Attached file is the lscpu output for Linux Kernel-4.16.2.

[linux_monkey · Accepted solution]

Your topology is now correct. As abucodonosor​ pointed out, the fix for this particular issue (applies to all parts with < 32 cores) went into the upstream 4.13 kernel and has been back-ported to RHEL 7.4 as of the late December update (just before the Spectre / Meltdown mitigation releases).

-Monkey

[iamdady]

Thanks a lot!