While it’s technically still the new kid on the block, the Compute Express Link (CXL) standard for host-to-device connectivity has quickly taken hold in the server market. Designed to offer a rich I/O feature set built on top of the existing PCI-Express standards – most notably cache-coherency between devices – CXL is being prepared for use in everything from better connecting CPUs to accelerators in servers, to being able to attach DRAM and non-volatile storage over what’s physically still a PCIe interface. It’s an ambitious and yet widely-backed roadmap that in three short years has made CXL the de facto advanced device interconnect standard, leading to rivals standards Gen-Z, CCIX, and as of yesterday, OpenCAPI, all dropping out of the race.
And while the CXL Consortium is taking a quick victory lap this week after winning the interconnect wars, there is much more work to be done by the consortium and its members. On the product front the first x86 CPUs with CXL are just barely shipping – largely depending on what you want to call the limbo state that Intel’s Sapphire Ridge chips are in – and on the functionality front, device vendors are asking for more bandwidth and more features than were in the original 1.x releases of CXL. Winning the interconnect wars makes CXL the king of interconnects, but in the process, it means that CXL needs to be able to address some of the more complex use cases that rival standards were being designed for.
To that end, at Flash Memory Summit 2022 this week, the CXL Consortium is at the show to announce the next full version of the CXL standard, CXL 3.0. Following up on the 2.0 standard, which was released at the tail-end of 2020 and introduced features such as memory pooling and CXL switches, CXL 3.0 focuses on major improvements in a couple of critical areas for the interconnect. The first of which is the physical side, where is CXL doubling its per-lane throughput to 64 GT/second. Meanwhile, on the logical side of matters, CXL 3.0 is greatly expanding the logical capabilities of the standard, allowing for complex connection topologies and fabrics, as well as more flexible memory sharing and memory access modes within a group of CXL devices.
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Author: Ryan Smith