LLC on multi-socket

By: Purple People Eater (, July 28, 2020 2:25 pm
Room: Moderated Discussions
I have a doubt about LLC and multi-socket CPUs. Let's say Intel but I'm interested too if it is different elsewhere.

Assume an N-socket CPU with DRAM attached to each socket as is usual. As I understand it, any given cache line lives in exactly one place in DRAM: let's call the socket associated with that the "home" socket. Any reads or writes to DRAM for that line will ultimately be served through the memory controller attached to the home socket.

How do the LLC's work for that line? Can the line appear only in one LLC at a time? If so, can it appear only in the home LLC? If it can appear in multiple LLCs, how is the flow when a non-home socket tries to read the line, and it is present and dirty in the LLC of some other non-home socket? Does the request go to the home socket which has to probe (or do a directory lookup) to find the line on other sockets?
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LLC on multi-socketPurple People Eater2020/07/28 02:25 PM
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            LLC on multi-socketAnon32020/07/29 09:13 AM
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  MESIF protocol and QPIDavid Kanter2020/07/28 09:54 PM
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