Index

Design

This document elaborates on some design decisions & the motivation behind them.

Microkernel

The main reason is to make it trivial to replace drivers, which is useful when isolating processes. e.g. any network operations could be proxied through a firewall, which can be implemented as a separate process. This is completely transparent to the client.

Another is to allow high-performance applications to directly integrate drivers, e.g a database could directly communicate with disks, reducing overhead & latency significantly.

Asynchronous I/O

So far, asynchronous I/O using ring buffers seems to be the best-performing on modern hardware, since it reduces privilege & context switches associated with blocking I/O. It also scales well with increasing workloads as more work will be done between each poll, i.e. batch size scales automatically.

Synchronous I/O is often easier to use & the right choice if the result is immediately needed. Since this type of I/O likely doesn’t need to be very performant it is implemented on top of the existing asynchronous interface.

Object-oriented interface

A minimal but powerful OO interface makes it easy to isolate & scale processes. For example, a job server can run a compile run on many different machines by providing a custom process table, which instead of creating a new process on the local machine will pick any machine as appropriate. It can also provide a file table which will gather outputs from any processes to a central location.

Multi-stage bootloader

While there are many powerful bootloaders, they also still leave much setup work to the kernel such as setting up the page tables. To simplify things & reduce the size of the kernel itself a separate bootloader is used. This loader passes a very easy to parse info structure to the kernel. It handles identity-mapping, loading of the kernel ELF binary & can pass any drivers to the kernel. It also tells the kernel which memory regions are free & useable as regular volatile RAM.