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#116 in Unix APIs
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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.
A highly configurable multi-layer BPF / user space hybrid scheduler.
scx_layered allows the user to classify tasks into multiple layers, and apply
different scheduling policies to those layers. For example, a layer could be
created of all tasks that are part of the
user.slice cgroup slice, and a
policy could be specified that ensures that the layer is given at least 80% CPU
utilization for some subset of CPUs on the system.
How To Install
Available as a Rust crate:
cargo add scx_layered
Typical Use Case
scx_layered is designed to be highly customizable, and can be targeted for specific applications. For example, if you had a high-priority service that required priority access to all but 1 physical core to ensure acceptable p99 latencies, you could specify that the service would get priority access to all but 1 core on the system. If that service ends up not utilizing all of those cores, they could be used by other layers until they're needed.
Yes. If tuned correctly, scx_layered should be performant across various CPU architectures and workloads.
That said, you may run into an issue with infeasible weights, where a task with a very high weight may cause the scheduler to incorrectly leave cores idle because it thinks they're necessary to accommodate the compute for a single task. This can also happen in CFS, and should soon be addressed for scx_layered.