SILICON | Loongson promises self-reliance with new architecture
Apr 21, 2021
China’s quest for a homegrown CPU
The global CPU market has been dominated by the x86 architecture for years, essentially controlled by two companies, Intel and AMD. For several years now Chinese companies have been trying to break this duopoly, with some success domestically but definitely not globally. Huawei and Phytium both used the Arm v8 architecture to create powerful 64-core server chips used in data centers and supercomputing. Under US pressure, it is difficult for either company to continue creating such chips. Hygon and Zhaoxin design x86 processors through joint ventures with AMD and VIA, although Hygon fell into geopolitical trouble as well. Another company, Sunway, has always used the lesser-known, US-designed Alpha architecture, but as far as I know Sunway processors were only ever used within the government. A few companies, most notably C-Sky and China Core, tried to promote their own architectures or variants of older ones like PowerPC into the commercial market. Both more or less failed and have since latched onto the much talked-about open-source RISC-V architecture. Alibaba acquired C-Sky in 2018. It’s now a leading RISC-V processor company under the name T-Head. Loongson has always used the MIPS architecture. MIPS ISA has an interesting history, but it is going out of fashion—even its owner, MIPS Technologies, has ditched it in favor of RISC-V. There has never been a successful Chinese architecture. C-Sky failed to scale and moved to RISC-V. Other companies that claim to be “made in China” have used or use existing open-source or licensable architectures. Starting from scratch to build an ISA is a big challenge. It’s faster to design your CPU based on a mature architecture, because there is an existing hardware and software ecosystem to latch onto. However, with Huawei, Phytium, Hygon, and Shenwei on the US entity list, China is worried that it doesn’t have a completely independent architecture. RISC-V may be a great platform for Chinese companies to go overseas with their designs, but it is a global initiative, and in some cases, China may want something that is totally its own. No patent infringements
You may be wondering if LoongArch infringes on patents from other architectures. To allay such fears, Loongson paid for a third-party IP agency last year to analyze whether LoongArch infringed on other architectures including Arm, x86, RISC-V, and MIPS. They concluded that the design is unique and independent, that its manual was clearly different to others’, and that it didn’t infringe on Chinese patents for any of the major international architectures. Perhaps the key phrase here is Chinese patents, rather than global. This may be something to keep an eye on. Loongson says they will analyze international patents as well but have so far concluded that the architecture is completely independent and controllable. It seems to me that in order to avoid patent infringements and at the same time support emulation of other architectures they have ended up increasing the complexity of their instruction-set: 2,000 instructions is more than other mainstream architectures. Loongson 3A5000
The Loongson 3A5000 CPU, announced last month, is already using this new architecture and has already been successfully “taped out,” and sent to a fabrication plant for production, at 12nm. This CPU is aimed at the PC market. The interesting thing here is the process node. Loongson has always used GlobalFoundries to tape out chips based on ST-Micro’s FD-SOI process. One might presume they would continue to use GlobalFoundries for the new generation chip, but they have not announced what process it uses. Some have said it will use the TSMC 12nm process , while others suggested it could be using SMIC , which now boasts the ability to tape out 12nm. SMIC may be not be ready for mass production yet, but for a test chip, this should not be a problem. This could be a Chinese architecture manufactured at a Chinese fab—just hearsay right now, but something to consider. TSMC or GlobalFoundries are still more likely, as SMIC 12nm would be new to the company, and SMIC has recently come under more restrictions from the US. It’s also worth noting that Loongson moving from 28nm in previous chips up to 12nm shows development in its design capabilities. It also has a new server chip 3C5000 using the same process but it is said to be much more powerful. Why not RISC-V? Since Wave Computing became MIPS Technologies and ditched the MIPS architecture in December, there have been rumors that Loongson would follow. Most in the industry surmised the company would move to RISC-V like many others have. RISC-V seems to be the easiest route for a company like Loongson, but there are some reasons why it might have chosen not to. First, there are other companies doing this, so it would be difficult to differentiate. Secondly, it’s clear Loongson wanted something 100% Chinese, not reliant on an international architecture. Finally, Loongson might be planning to follow the RISC-V model and actually open the architecture. According to its press release, once the IP patent situation is confirmed globally, they plan on creating a LoongArch Alliance where members can access the architecture and Loongson IP cores for free. While the company did not say the instruction set will be open to members, it is certainly possible. It is rumored though that the company will join the RISC-V consortium. Prior to the LoongArch announcement, executives have said they are “ looking forward to join the open-source instruction consortium .” Most thought this meant RISC-V, but they could have been alluding to their own alliance. I wouldn’t be surprised if the company joined RISC-V. Its own architecture could be used within China for military or government applications, while RISC-V would be a better platform for Loongson to finally go global. Time will tell
“Only by achieving independence in the root of the instruction system can the software ecosystem chains be broken,” Loongsoon management said in its press release. Such statements make it clear that the main purpose of LoongArch is for China to have its own fully independent instruction-set architecture. Since C-Sky moved to RISC-V, this hasn’t been the case. While I do not see LoongArch becoming a globally competitive architecture, as ecosystems are difficult to build up, it could be another string in China’s self-reliance bow. It will also be interesting to see how the LoongArch Alliance develops. Will it open the instruction-set architecture? If cores designs are free, is that just for research or for commercial use as well? This whole initiative definitely has government support. Loongson came out of the Institute of Computing Technology, China Academy of Sciences, which is still a major shareholder, and a RISC-V consortium member, with one person on its board. I will be keeping an eye on whether LoongArch infringes on any global patents, any processor benchmarks out there, how its alliance develops, and whether it does make a move to RISC-V in the end as well. It will likely be used in government and military PC and server applications, but can it move beyond that? Time will tell.