26d6d530f0
Evaluate the number of voluntary context switches per second (nvcsw/sec) for each task using an exponentially weighted moving average (EWMA) with weight 0.5, that allows to classify interactive tasks with more accuracy. Using a simple average over a period of time of 10 sec can introduce small lags every 10 sec, as the statistics for the number of voluntary context switches are refreshed. This can result in interactive tasks taking a brief time to catch up in order to be accurately classified as so, causing for example short audio cracks, small drop of 5-10 fps in games, etc. Using a EMWA allows to smooth the average of nvcsw/sec, preventing short lags in the interactive tasks, while also preventing to incorrectly classify as interactive tasks that may experience an isolated short burst of voluntary context switches. This patch has been tested with the usual test case of playing a videogame while running a parallel kernel build in the background. Without this patch the short lag every 10 sec is clearly noticeable, with this patch applied the game and audio run smoothly. Signed-off-by: Andrea Righi <andrea.righi@canonical.com> |
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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
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.