Run command on K3's AI cores

Utility to run a command with arguments on the A100 "AI" cores on SpacemiT K3.

Quick start

$ git clone https://github.com/brucehoult/k3_ai
$ cd k3_ai
$ make
$ ai bash

Usage

ai cmd arg1 arg2 ...

aix path arg1 arg2 ...

Normally prefer to use ai. This is a shell script that converts a bare program name to the absolute path of the executable and then chains to aix. It's about 1ms slower than calling aix directly.

aix is a tiny assembly language program that needs the absolute or relative path of the program to run. It is written to be pure asm using only syscalls, no libraries, no dynamic linker, so as to be really sure that nothing has used any RVV instructions in this process, and therefore no decisions have been made based on the X100 core's shorter VLEN.

Examples

# just run a single program on the A100 cores
ai as hello.s -o hello.o

# same thing but maybe 1ms faster
aix /usr/bin/as hello.s -o hello.o

# run a whole build. All processes started by `make` will run on the A100 cores.
ai make -j8 test

# start a shell on the A100 cores. All programs run from it will be run only on the A100 cores
ai bash

Why you need it

The K3 has eight high performance Out-of-Order X100 cores with RISC-V vector length of 256 bits. These cores are what all normal Linux programs run on.

There are also eight lower performance in-order A100 "AI" cores similar to the X60 cores in the SpacemiT K1/M1 chips, but with long 1024 bit vector registers and ALU.

The "AI" cores can actually run all normal Linux programs. On standard scalar code they have approximately 40% the performance of the main X100 cores, but on certain kinds of vectorised code (for example Llama) they have considerably higher performance.

Even ignoring vectorised code, the A100 cores by themselves have more computing power than any previous RISC-V computer under $1000, including those using the Allwinner D1, StarFive JH7110, THead TH1520, SpacemiT K1/M1, or even Eswin EIC7700x.

As such, it is well worth using the A100 cores to run normal programs and adding 40% to the overall power of a K3 computer.

Because of the different vector length, it is dangerous to move a program between X100 and A100 cores -- in either direction -- once it has been started.

SpacemiT provides a mechanism to move an existing running program from the X100 cores to the A100 cores by writing the PID of the process to /proc/set_ai_thread but that is dangerous depending on what that process has already done.

This utility creates a new process and then moves it to the A100 cores before it has done anything dangerous, and then does EXEC() on the program you really wanted to run.