LoongArch Adds Simultaneous Multi-Threading, SIMD/Vector Extensions

China's Loongson continues preparing the software support for their upcoming 3A6000 processors that will feature several new capabilities over their inaugural LoongArch-based 3A5000 series.

As written about a few weeks ago, Loongson 3A6000 brings SMT support similar to Intel, AMD, and POWER processors. LoongArch is rolling out 2-way SMT with these upcoming Chinese processors to double the thread count. At least for what's been mentioned in Linux patch chatter, the 3A6000 will feature four core / eight thread SKUs. The necessary kernel support for LoongArch SMT has been submitted for Linux 6.5.

Also being added to Linux 6.5 for the LoongArch architecture code is support for compiling the Linux kernel with Clang. ClangBuiltLinux has long been around now for x86_64 and AArch64 while now with Linux 6.5 is the necessary kernel changes for compiling under Clang though there remain some patches yet to be merged to the LLVM/Clang compiler for pushing things over the finish line. The initial LoongArch support was merged back in LLVM 15.

Linux 6.5 is also enabling LoongArch SIMD/vector extension support. The LoongArch vector extensions are 128-bit LSX (Loongson SIMD eXtension) and 256-bit LASX (Loongson Advanced SIMD eXtension). The Linux kernel needs changes just for handling exceptions and context save/restore around these LSX/LASX extensions. It will be interesting to see how these vector extensions perform with the upcoming LoongArch processors.

The pull of LoongArch CPU changes for Linux 6.5 also include enabling hardware page table walker support, junp-label support, Rethook and Uprobes support, and various other improvements and fixes.

At least based on prior announcements by Loongson, the upcoming 3A6000 series processors are said to be comparable to 10th Gen Intel Core processors but remains to be seen if any of these new CPUs will reach western markets for hardware testing.