f0ece7af6b
Trigger the user-space scheduler only upon a task's CPU release event (avoiding its activation during each enqueue event) and only if there are tasks waiting to be processed by the user-space scheduler. This should save unnecessary calls to the user-space scheduler, reducing the overall overhead of the scheduler. Moreover, rename nr_enqueues to nr_queued and store the amount of tasks currently queued to the user-space scheduler (that are waiting to be dispatched). Signed-off-by: Andrea Righi <andrea.righi@canonical.com> |
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| .. | ||
| scx_layered | ||
| scx_rustland | ||
| scx_rusty | ||
| meson.build | ||
| README.md | ||
RUST SCHEDULERS
Introduction
This directory contains schedulers with user space rust components.
This document will give some background on each scheduler, including describing the types of workloads or scenarios they're designed to accommodate. For more details on any of these schedulers, please see the header comment in their main.rs or *.bpf.c files.
Schedulers
This section lists, in alphabetical order, all of the current rust user-space schedulers.
scx_layered
Overview
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.
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.
Production Ready?
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.
scx_rusty
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.
Typical Use Case
Rusty is designed to be flexible, and accommodate different architectures and workloads. Various load balancing thresholds (e.g. greediness, frequenty, 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. Rusty by default 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.