The P5600 core is being touted as supporting up to six cores in a cache-coherent link, most likely similar to ARM's CCI-400.
The CCI-400 is not relevant here. In both MIPS and ARM worlds CPUs are now multi cores capable out of the box. One cluster can be configured from 1 to 4 cores typically, and here for this latest MIPS up to 6. The L2 management is handled as part of the cluster, which also typically supports coherency with external hardware accessing the L2 through one or several coherency port(s). The L1 cache(s), the L2 and the hardware are kept coherent inside a cluster (with some limitations at times on the low end, there are variants). All this can be taken for granted at the high-end, as here.
Now what the CCI-400 does is different: it extends coherency management between several clusters. This is very important in the ARM world because of the big.LITTLE scheme: you want the big cluster and little cluster to be kept coherent to speed-up and easy the transition between the low-power and high performance modes (that also helps when all cores are used at all times, as the OS can migrate tasks between cores more efficiently).
Rising defect densities have created a situation where — for the first time ever — 20nm wafers won't be cheaper than the 28nm processors they're supposed to replace.
The economic part is often left out on tech sites discussions, but it matters a lot. Up to now we had a sustainable situation where the cost of new processes increased regularly, but at the same time eventually the cost of the new process was lower. This allowed to get all on board and to also increase the reachable market, to get more revenues. That's why we have small micro-controllers everywhere nowadays.
Now when the cost of new processes increases, only the part of the market that trully need the improved density and performance will move on. And that's only a small part of the whole market. So we will have increasing costs, with a reducing addressable market. Double whammy. Expect end prices for high performance to rise quickly. That may slow down things significantly.
We'll see how it develops soon, but I would expect the economic to bite before we reach tech limits.
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