scx-upstream/scheds/rust/scx_bpfland
Andrea Righi 5a08855a86 scx_bpfland: always honor average nvcsw in lowlatency mode
Keep evaluating the average number of voluntary context switches for
each task when lowlatency mode is enabled, even when interactive tasks
classification is disabled (via `-c 0`).

The average nvcsw is also used in lowlatency mode to evaluate the
proportional bonus to the tasks' deadline and it shouldn't be ignored
when interactive tasks classification is disabled. Moreover, make sure
that such bonus never exceeds the starvation threshold.

Keep in mind that it is still possible to disable the periodic average
nvcsw evaluation with `-c 0`, without specifying `--lowlatency`.

Fixes: 6a22853 ("scx_bpfland: introduce --lowlatency option")
Signed-off-by: Andrea Righi <andrea.righi@linux.dev>
2024-08-24 10:42:22 +02:00
..
src scx_bpfland: always honor average nvcsw in lowlatency mode 2024-08-24 10:42:22 +02:00
build.rs scx_bpfland: update copyright info 2024-08-14 16:17:54 +02:00
Cargo.lock Version: Cargo.lock 2024-08-21 06:45:19 -10:00
Cargo.toml Version: v1.0.3 2024-08-21 06:42:11 -10:00
LICENSE scheds: introduce scx_bpfland 2024-06-27 17:28:42 +02:00
meson.build scx_bpfland: properly integrate with meson build 2024-06-28 21:37:00 +02:00
README.md scheds: introduce scx_bpfland 2024-06-27 17:28:42 +02:00
rustfmt.toml scheds: introduce scx_bpfland 2024-06-27 17:28:42 +02:00

scx_bpfland

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_bpfland: a vruntime-based sched_ext scheduler that prioritizes interactive workloads.

This scheduler is derived from scx_rustland, but it is fully implemented in BPF with minimal user-space Rust part to process command line options, collect metrics and logs out scheduling statistics. The BPF part makes all the scheduling decisions.

Tasks are categorized as either interactive or regular based on their average rate of voluntary context switches per second. Tasks that exceed a specific voluntary context switch threshold are classified as interactive. Interactive tasks are prioritized in a higher-priority queue, while regular tasks are placed in a lower-priority queue. Within each queue, tasks are sorted based on their weighted runtime: tasks that have higher weight (priority) or use the CPU for less time (smaller runtime) are scheduled sooner, due to their a higher position in the queue.

Moreover, each task gets a time slice budget. When a task is dispatched, it receives a time slice equivalent to the remaining unused portion of its previously allocated time slice (with a minimum threshold applied). This gives latency-sensitive workloads more chances to exceed their time slice when needed to perform short bursts of CPU activity without being interrupted (i.e., real-time audio encoding / decoding workloads).

Typical Use Case

Interactive workloads, such as gaming, live streaming, multimedia, real-time audio encoding/decoding, especially when these workloads are running alongside CPU-intensive background tasks.

In this scenario scx_bpfland ensures that interactive workloads maintain a high level of responsiveness.

Production Ready?

The scheduler is based on scx_rustland, implementing nearly the same scheduling algorithm with minor changes and optimizations to be fully implemented in BPF.

Given that the scx_rustland scheduling algorithm has been extensively tested, this scheduler can be considered ready for production use.