scx-upstream/scheds/rust/scx_rustland

scx_rustland

This is a single user-defined scheduler used within sched_ext, which is a Linux kernel feature which enables implementing kernel thread schedulers in BPF and dynamically loading them. Read more about sched_ext.

Overview

scx_rustland is made of a BPF component (dispatcher) that implements the low level sched-ext functionalities and a user-space counterpart (scheduler), written in Rust, that implements the actual scheduling policy.

The BPF dispatcher is completely agnostic of the particular scheduling policy implemented in user-space. For this reason developers that are willing to use this scheduler to experiment scheduling policies should be able to simply modify the Rust component, without having to deal with any internal kernel / BPF details.

How To Install

Available as a Rust crate: cargo add scx_rustland

Typical Use Case

scx_rustland is designed to be "easy to read" template that can be used by any developer to quickly experiment more complex scheduling policies, that can be fully implemented in Rust.

Production Ready?

Not quite. For production scenarios, other schedulers are likely to exhibit better performance, as offloading all scheduling decisions to user-space comes with a certain cost.

However, a scheduler entirely implemented in user-space holds the potential for seamless integration with sophisticated libraries, tracing tools, external services (e.g., AI), etc. Hence, there might be situations where the benefits outweigh the overhead, justifying the use of this scheduler in a production environment.

Demo

scx_rustland-terraria

For this demo the scheduler includes an extra patch to impose a "time slice penalty" on new short-lived tasks. While this approach might not be suitable for general usage, it can yield significant advantages in this specific scenario.

The key takeaway is to demonstrate the ease and safety of conducting experiments like this, as we operate in user-space, and we can accomplish everything simply by modifying the Rust code, that is completely abstracted from the underlying BPF/kernel internal details.