Latest Loongson chip is another step in China's long road to semiconductor freedom

Homegrown processor looks like RISC-V-MIPS fan fiction

Comment China is slowly achieving its long-term goal of semiconductor self-sufficiency – homegrown chips for its computing devices, in other words.

The Loongson processor family, developed in the Middle Kingdom, frees China from the hegemony of foreign chip makers, and gives the country more control of its information-technology assets, the namesake chip company boldly stated lately.

Loongson further goes on to berate foreign chip makers as dictator-type entities using CPU architectures as a means of control.

China stepped up investments in developing homegrown processors in the early 2000s. Loongson, which was conceived as a MIPS-compatible family in 2001 by the government-run Chinese Academy of Sciences, has driven chip development via processors codenamed Godson and Loongson, which have been used in PCs and supercomputers.

Its latest component is a quad-core 2.5GHz, 35W processor dubbed the 3A5000, which was designed for use in desktops, servers, kiosks, and appliances, according to the designer's website. There's no mention of laptops. It delivers a peak performance of 160 giga-FLOPS though doesn't state the precision. We're also told the CPU cores are four-issue out-of-order designs, each with 64KB L1 data and instruction caches, 256KB of L2 cache, and share a 16MB L3 cache.

The 3A5000 is said to be 50 per cent faster and 30 per cent more power efficient than its predecessor, the 3A4000. The chip also has 128 and 256-bit vector math units, NUMA support, and more bits and pieces.

The 16-core 3C5000L – which is four 3A5000 chips in a single package – is designed for servers, and delivers a peak performance of 560Gflops.

The chips have pretty standard features – table stakes, even – and won't strongly compete with what the x86 or Arm world has to offer. Yet they do provide a stepping stone for China to develop faster processors as the country cuts its reliance on foreign semiconductor suppliers.

The 3A5000 is "independently designed without foreign authorization, and it integrates x86, Arm and other international mainstream command systems," the chipmaker boasted. By that, it's believed the biz means that its CPU cores feature circuitry that aids in the emulation and binary translation of non-Loongson instruction sets, such as x86, into something that runs natively.

There has been much debate about the originality of LoongArch – the 3A5000's CPU core architecture – and Loongson's Huacai Chen said a few weeks ago in a memo to top Linux kernel developers that LoongArch is similar to MIPS and RISC-V.

It was suspected Loongson had taken parts of MIPS and RISC-V that it liked the most and melded them together into a hybrid architecture for the 3A5000. It helps that MIPS and RISC-V are both quite, well, RISC-y, allowing Loongson to combine the two, along with a ton of custom instructions – some publicly documented and some not – to form LoongArch.

"LoongArch is a new RISC ISA, which is a bit like MIPS or RISC-V. LoongArch includes a reduced 32-bit version (LA32R), a standard 32-bit version (LA32S) and a 64-bit version (LA64)," Huacai said.

Earlier this year, a Linux kernel developer pointed out that the kernel code submitted by Loongson to support the 3A5000 and other LoongArch processors was very similar to the code used to drive MIPS systems, suggesting Loongson and MIPS were quite alike operationally.

You keep saying 'not MIPS,' and yet all I see is a blind copy of the MIPS code

"You keep saying 'not MIPS,' and yet all I see is a blind copy of the MIPS code," said Marc Zyngier in a post to the Linux kernel board in late August.

"This is still the same antiquated, broken MIPS code, only with a different name."

The 3A5000 can be used to run x86 Windows software natively-ish: Loongson said it successfully implemented a translator that allows even Windows drivers to work transparently. LoongArch's predecessor, the obviously MIPS64-based LoongISA, featured instructions to handle and accelerate the translation of x86 and Arm code into MIPS instructions, and it seems clear this technology has been carried over into LoongArch.

You can find LoongArch partially documented here, and we note that its instruction encoding at least isn't the same as MIPS, though with both being RISC ISAs, there are similarities.

The chip also runs Linux variants including Loongnix, which is a fork of CentOS Linux OS.

Given China has been repeatedly accused of stealing intellectual property, Loongson said a "domestic third-party intellectual property evaluation agency" assessed that LoongArch is "obviously different" from architectures like Alpha, MIPS, Arm, POWER, RISC-V and x86.

Historically, Loongson chips have been developed around the MIPS architecture. Meanwhile, MIPS has thrown its weight behind the RISC-V approach. And the Chinese cloud giant Alibaba has just open-sourced a bunch of RISC-V CPU designs. There could be interesting times ahead. ®

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