IBM Open-Sources Power ISA, Shares CPU, OpenCAPI Reference Designs

IBM has been turning towards open source as a method for reinvigorating its hardware business and stoking interest in its own ecosystem. In addition to open-sourcing the Power ISA, the company has also contributed designs for its Open Coherent Accelerator Processor Interface (OpenCAPI) and Open Memory Interface (OMI). These are the interface protocols that attach the CPU to the rest of the system, and they’re critical to making the total project work. OpenCAPI and OMI are both architecture-agnostic and could theoretically be adapted for usage in both x86 and Power systems, should vendors build compatible solutions.

Ken King, general manager of OpenPower at IBM, told Next Platform that the plan to open source the ISA had been a long time coming:

We started OpenPower six years ago because the industry was seeing the decline of Moore’s Law, and we were seeing the need for more powerful systems to support HPC, artificial intelligence, and data analytics. We needed to find other ways to drive system performance, and with limitations on the processor, the ability to integrate and innovate up and down the stack was becoming more critical. This led to things like NVLink with Nvidia, a close relationship with Mellanox on interconnects, and OpenCAPI for other devices, and we have seen some progress here.

But we are also seeing a shift in the industry, with companies moving to more open hardware. IBM opening up Power to the point where we would license the CPU RTL to others so they could design their own processors was limited in its effect because there were not that many people who wanted to spend many hundreds of millions of dollars – not for license fees, but for full development – to create their own high-end CPU. We did make some progress in opening up our reference designs, and there are over 20 vendors who are now making Power-based systems.

We are seeing interesting developments with the nascent RISC-V architecture, and hyperscalers are hiring their own chip designers and building their own CPUs and interconnects. They are getting into the hardware space, even if they are not going to be hardware vendors, to drive that performance.

Under the Linux Foundation, IBM and other members will vote on the future of the standard, including feature set expansions and new capabilities. IBM can continue to make changes to its own ISA for its own purposes, but all other modifications require a membership vote. Members are required to maintain compatibility with the base ISA. Permission to make a non-compliant change will require a unanimous vote. King has openly stated that he hopes Intel will be willing to explore the benefits of using OpenCAPI now that the standard is available in this method, leading to a convergence of support between OpenCAPI and CXL, Intel’s competing interconnect standard.

IBM is hoping that completely open-sourcing the ISA will spur adoption and development. There’s some reason for optimism. Another open-source ISA, RISC-V, has been generating many headlines and interest from various silicon vendors. Current RISC-V CPUs, however, are all low-end embedded hardware. In theory, Power might be an easier lift if its toolchains are more mature and better-featured.

“The opening of the Power ISA, an architecture with a long and distinguished history, will help the open hardware movement continue to gain momentum,” Mateo Valero, Director of Barcelona Supercomputing Center, told InsideHPC. “BSC, which has collaborated with IBM for more than two decades, is excited that IBM’s announcements today provide additional options to initiatives pursuing innovative new processor and accelerator development with freedom of action.”

Though it hasn’t spent much time in the limelight of late, Power was once a major challenger to Intel’s competing x86 architecture in the server world. In recent years, the OpenPower initiative has enjoyed support from a number of companies, with over 250 members as of 2016. Today, it still enjoys market share in the HPC space — the Summit and Sierra supercomputers are #1 and #2 in the world. The third machine is based on custom Sunway architecture. The highest-powered x86 computer is China’s Tianhe-2A, based on the Xeon E5-2692v2. There’s nothing stopping a company from taking Power into new markets (at least in theory), though it would be quite difficult to convince smartphone vendors to rally around Power as opposed to ARM. Still, open-sourcing the architecture can’t hurt its uptake effort.

We’d expect to see the most energy and excitement around Power in servers and HPC because that’s where the core of IBM’s efforts have historically been focused. But we wouldn’t be surprised to see the ISA popping up in other places, either.