Each to their own but if you read and understand the comment above they're describing a dedicated OS for the task .. so think about what you'd choose to write a small task dedicated OS with.
Simple C is most likely, ASM is possible, a language such as OCaml generating C to hook into the low level buffers would be intriguing ... the list is long and largely determined by the experience preference of whoever tackles it.
The major features for performance are to allocate and manage all memory from the start .. determine your thresholds of performance and put everything required together on cold start so as to avoid any thrashing at runtime.
Simple C is most likely, ASM is possible, a language such as OCaml generating C to hook into the low level buffers would be intriguing ... the list is long and largely determined by the experience preference of whoever tackles it.
The major features for performance are to allocate and manage all memory from the start .. determine your thresholds of performance and put everything required together on cold start so as to avoid any thrashing at runtime.