Comprehensive Threadripper tests - memory vs cpu freq at capped power

Gerald Henriksen ghenriks at
Thu Aug 23 17:04:13 PDT 2018

On Thu, 23 Aug 2018 23:17:29 +0300, you wrote:

>The Threadripper discussion has been very interesting.
>Will these adjustments to NUMA for Threadripper's topography also apply to Epyc also? Or will more nuanced work need to be done once an Epyc system becomes available?

Epyc doesn't have the limitations that Threadripper has, so the
changes aren't needed.

The basic explanation is this.

With both Threadripper and Epyc the module you plug into the
motherboard actually contains 4 chips, connected together.

Each chip has 2 memory controllers.

In Epyc all 4 chips have their memory controllers enabled/connected,
thus allowing each chip to access memory directly.

With the original version of Threadripper only 2 of the 4 chips were
active, and the 2 active chips had their memory controllers enabled
allowing direct access.

The new version of Threadripper has all 4 chips active BUT only 2
chips have memory controllers enabled.  Thus the 2 chips without
active memory controllers are forced to access memory through the
other 2 chips.  This is what is requiring the changes.

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