Interconnect between per-core L2 and L3 in Core i7

Question

The Intel core i7 has per-core L1 and L2 caches, and a large shared L3 cache. I need to know what kind of an interconnect connects the multiple L2s to the single L3. I am a student, and need to write a rough behavioral model of the cache subsystem. Is it a crossbar? A single bus? a ring? The references I came across mention structural details of the caches, but none of them mention what kind of on-chip interconnect exists.

Thanks,

-neha

Answer 1

Modern i7's use a ring. From Tom's Hardware:

Earlier this year, I had the chance to talk to Sailesh Kottapalli, a senior principle engineer at Intel, who explained that he’d seen sustained bandwidth close to 300 GB/s from the Xeon 7500-series’ LLC, enabled by the ring bus. Additionally, Intel confirmed at IDF that every one of its products currently in development employs the ring bus.

Your model will be very rough, but you may be able to glean more information from public information on i7 performance counters pertaining to the L3.