![]() ![]() ![]() (Loads that miss in cache default to loading into Exclusive state so a separate store won't have to do an RFO for the same line). In a similar case, core #1 could have silently dropped the line without having modified it, if it had only gotten Exclusive ownership but never written it. BeeOnRope has an answer that with a similar breakdown into steps that covers uops and the store buffer, as well as MESI / RFO. This is super hand-wavy do not take my word for it on the exact details, but the general concept of sending messages like share-request, RFO, or write-back, is the right mental model. (Worst case distance = basically all the way around the ring, instead of half, for a bidirectional ring.) IDK if one ring bus message can be read directly by Core #0 as well as the relevant slice of 元 cache, or if the message might have to go all the way to the 元 slice and then to core #0 from there. The message arrives at the ring bus stop for core #1, and gets its L2 or L1d to write back that line. 元 cache logic in that slice of 元 will generate a message to ask core #1 to write back that line. Otherwise, 元 tags tell it that core #1 has exclusive ownership of a line: Exclusive, may have been promoted to Modified = dirty. If it found tag = Shared at this point, the response could go back over the bidirectional ring bus with the data. That slice of 元 gets the message, checks its tags. Read misses in L1d and L2 cache on core #0, resulting in is sending a request on the ring bus to the 元 slice that contains that line (indexing via a hash function on some physical address bits) That line is in Modified state on core #1. Which cache mapping technique is used in intel core i7 processor?įor example, a Sandybridge-family CPU with a ring bus (modern client chips, server chips up to Broadwell). the shared inclusive 元 cache in Intel CPUs ( before Skylake server) lets 元 tags act as a snoop filter as well as tracking the MESI state, they also record which core # (if any) has a private copy of a line. ![]() MESI states for each cache line can be tracked / updated with messages and a snoop filter (basically a directory) to avoid broadcasting those messages, which is what Intel (MESIF) and AMD (MOESI) actually do.Į.g. MESI is defined in terms of snooping a shared bus, but no, modern CPUs don't actually work that way. ![]()
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