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Are there CPU architectures where 8 cores share a L2 cache? I'm not aware of any though I can think of several where 4 cores share a L2 cache, though those ten
by Symmetry 5y ago
Are there CPU architectures where 8 cores share a L2 cache? I'm not aware of any though I can think of several where 4 cores share a L2 cache, though those tend to be pretty lightweight cores. More often you see issues with the L3 cache being shared between 8 cores or no as with Zen 2 versus Zen 3. And since only lightweight cores tend to share L2s this isn't really an issue in terms of replacing heavyweight cores with lightweight ones. Mostly, though when I think about sharing data between 8 cores I tend to be concentrating on making sure it ends up as S in MESI, MOESI, MESIF or whatever cache coherency protocol the chip is using.
- jeffbee 5y agoSure, POWER9 offers pairs of SMT8 cores sharing L2 caches, that's 16 thread contexts presented to software that are all sharing an L2 cache domain. Intel "Tremont" Atom has a shared L2 cache for a module of up to 4 cores. Maybe that is the one you allude to as lightweight.
- Symmetry 5y agoYes, there are clearly architectures where 8 threads share a L2$. L1$ too in both recent POWER SMT8 cores and SPARC Niagras. Yes, Intel Atoms were one of the examples I was thinking of regarding 4 cores sharing an L2$. One can quibble about what counts as a "core" when you're talking about POWER9 or Bulldozers but even being generous I don't think there's ever been a design where 8 cores all share the same L2$.