“This working group is about making sure that the train tracks come together and they actually attach.īoth Bowman and Pappas have talked to us within the last few months in the stories mentioned above about using CXL as a potential mount point for Gen-Z fabrics inside of servers, and we suspect that this is how they will carve it up until long after Gen-Z silicon is out in volume. “You have probably seen that image of two train tracks coming from two different places trying to link, and they miss,” Pappas tells The Next Platform. (Which seems appropriate, if you think about it.) To be specific, they have put together a joint working group to hammer out the differences try to keep these technologies on a coherent path. They have decided to not have any hatchets at all and to work so that CXL and Gen-Z can interoperate and interconnect where appropriate. Or, more precisely, they didn’t even buy the hatchets to later bury them. (We drilled down into the Gen-Z switching chippery that HPE has cooked up back in September 2019 as well, and have also reviewed the Gen-Z memory server that the Gen-Z consortium is prototyping to create pooled main memory.)īut, under a memorandum of understanding signed by Kurtis Bowman, president of the Gen-Z consortium and also director of server architecture and technologies at Dell, and Jim Pappas, chairman of the CXL consortium and also director of technology initiatives at Intel, these two potentially warring camps have buried the hatchets. Well, the rules of economics, perhaps, suggest that CXL will be cheaper than Gen-Z, mostly because of the silicon photonics that is involved with long-haul coherence. Similarly there was no rule that said Gen-Z could not be used as a protocol within a server node. There was no rule that said CXL could not be extended out beyond a server’s metal skin to provide coherent memory access across multiple server nodes in one, two, or maybe three racks ( as PCI-Express switching interconnects like those from GigaIO are doing, for instance). Call it a harmonic convergence.ĬXL and its coherent memory interconnect were designed to link processors to their accelerators and memory class storage within a system, and Gen-Z was primarily designed as a memory fabric that could have lots of different compute engines hanging off it, sharing great gobs of memory of various kinds. We did a very deep dive on CXL here at the same time, which was again a coincidence. This is why the same week we hosted The Next I/O Platform event in San Jose last September – a happy coincidence, not planning – all of the members of the key coherency efforts – the Compute Express Link (CXL) from Intel, the Coherent Accelerator Interface (CAPI) and OpenCAPI superset from IBM, the Cache Coherence Interconnect for Accelerators (CCIX) from Xilinx, and the Infinity Fabric from AMD, the NVLink interconnect from Nvidia, and the Gen-Z interconnect from Hewlett Packard Enterprise and backed heavily and early by Dell – all got together to back Intel’s CXL protocol interconnect, itself a superset of PCI-Express 5.0, for linking processors to accelerators and sharing their memories. The reason is that we don’t have time for that nonsense, and with the economic very likely heading into recession globally, we have even less time for such shenanigans and ego. It perhaps took longer than it might otherwise – it is hard to rewrite history.īut what we can tell you – and what we have discussed for the past several months – is that the warriors who lived through those Bus Wars have learned from the history they created, and they don’t have any stomach for a protracted battle over transports and protocols for providing memory coherence across hybrid compute engines. The fighting among vendors to create standards that they controlled ultimately resulted in the creation of the PCI-X and PCI-Express buses that have dominated in servers for two decades, as well as the offshoot InfiniBand interconnect, which was originally intended as a universal switched fabric to connect everything at high bandwidth and low latency. To one way of looking at it, a reprise of the Bus Wars from days gone by in the late 1980s and early 1990s would have been a lot of fun.
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