Now with eight cores per CCX, since launch, AMD has been extremely coy about telling anyone publicly how those cores are connected together. When asked at launch if the cores in a Zen 3 eight-core CCX were fully connected, AMD’s general attitude was ‘Not quite, but close enough’. This would mean something between a ring and something between an all-to-all design, but more verging on the latter.
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In our testing, our results show that while AMD’s core complex is not an all-to-all connection, it also doesn’t match what we would expect from ring latencies. Simply put, it’s got to be more than a ring. AMD has been very coy on the exact details of their CCX interconnect – by providing a slide saying it’s a ring reinforces the fact that it’s not an all-to-all interconnect, but we’re pretty sure it’s some form of a bisected ring, a detail that AMD has decided to leave out of the presentation.