a76778a4ab
When hotplugging CPUs in rapid succession, scx_rusty would crash with: ``` scx_bpf_error (Failed to lookup dom[4294967295] ``` The root cause is if the scheduler is restarted fast enough, a task on a previously hotplugged CPU may not have moved off that CPU yet. Thus, the CPU -> domain map would contain an invalid domain (u32::max) and we would fail to lookup the domain correctly in rusty_select_cpu for prev_cpu. To fix this, if the CPU is offline, we do not try to allocate to the same NUMA node (assuming hotplug is a rare operation) beyond domestic domain. Instead we use greedy allocation - first idle, then busy - then any CPU. |
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scx_rusty
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
A multi-domain, BPF / user space hybrid scheduler. The BPF portion of the scheduler does a simple round robin in each domain, and the user space portion (written in Rust) calculates the load factor of each domain, and informs BPF of how tasks should be load balanced accordingly.
How To Install
Available as a Rust crate: cargo add scx_rusty
Typical Use Case
Rusty is designed to be flexible, accommodating different architectures and workloads. Various load balancing thresholds (e.g. greediness, frequency, etc), as well as how Rusty should partition the system into scheduling domains, can be tuned to achieve the optimal configuration for any given system or workload.
Production Ready?
Yes. If tuned correctly, rusty should be performant across various CPU architectures and workloads. By default, rusty creates a separate scheduling domain per-LLC, so its default configuration may be performant as well. Note however that scx_rusty does not yet disambiguate between LLCs in different NUMA nodes, so it may perform better on multi-CCX machines where all the LLCs share the same socket, as opposed to multi-socket machines.
Note as well that 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_rusty.