scheds: introduce scx_bpfland
Overview
========
This scheduler is derived from scx_rustland, but it is fully implemented
in BFP with minimal user-space Rust part to process command line
options, collect metrics and logs out scheduling statistics.
Unlike scx_rustland, all scheduling decisions are made by the BPF
component.
Motivation
==========
The primary goal of this scheduler is to act as a performance baseline
for comparison with scx_rustland, allowing for a better assessment of
the overhead caused by kernel/user-space interactions.
It can also be used to deploy prototypes initially tested in the
scx_rustland scheduler. In fact, this scheduler is expected to
outperform scx_rustland, due to the elimitation of the kernel/user-space
overhead.
Scheduling policy
=================
scx_bpfland is a vruntime-based sched_ext scheduler that prioritizes
interactive workloads. Its scheduling policy closely mirrors
scx_rustland, but it has been re-implemented in BPF with some small
adjustments.
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 DSQ, while
regular tasks are placed in a lower-priority DSQ. Within each queue,
tasks are sorted based on their weighted runtime, using the built-in scx
vtime ordering capabilities (scx_bpf_dispatch_vtime()).
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).
Results
=======
According to the initial test results, using the same benchmark "playing
a videogame while recompiling the kernel", this scheduler seems to
provide a +5% improvement in the frames-per-second (fps) compared to
scx_rustland, with video games such as Cyberpunk 2077, Counter-Strike 2
and Baldur's Gate 3.
Initial test results indicate that this scheduler offers around a +5%
improvement in frames-per-second (fps) compared to scx_rustland when
using the benchmark "playing a video game while recompiling the kernel".
This improvement was observed in games such as Cyberpunk 2077,
Counter-Strike 2, and Baldur's Gate 3.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
2024-06-24 06:56:03 +01:00
# scx_bpfland
This is a single user-defined scheduler used within [sched_ext ](https://github.com/sched-ext/scx/tree/main ), which is a Linux kernel feature which enables implementing kernel thread schedulers in BPF and dynamically loading them. [Read more about sched_ext ](https://github.com/sched-ext/scx/tree/main ).
## Overview
scx_bpfland: a vruntime-based sched_ext scheduler that prioritizes interactive
workloads.
2024-09-07 00:12:33 +01:00
This scheduler is derived from scx_rustland, but it is fully implemented in BPF.
It has a minimal user-space Rust part to process command line options, collect
metrics and log out scheduling statistics. The BPF part makes all the
scheds: introduce scx_bpfland
Overview
========
This scheduler is derived from scx_rustland, but it is fully implemented
in BFP with minimal user-space Rust part to process command line
options, collect metrics and logs out scheduling statistics.
Unlike scx_rustland, all scheduling decisions are made by the BPF
component.
Motivation
==========
The primary goal of this scheduler is to act as a performance baseline
for comparison with scx_rustland, allowing for a better assessment of
the overhead caused by kernel/user-space interactions.
It can also be used to deploy prototypes initially tested in the
scx_rustland scheduler. In fact, this scheduler is expected to
outperform scx_rustland, due to the elimitation of the kernel/user-space
overhead.
Scheduling policy
=================
scx_bpfland is a vruntime-based sched_ext scheduler that prioritizes
interactive workloads. Its scheduling policy closely mirrors
scx_rustland, but it has been re-implemented in BPF with some small
adjustments.
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 DSQ, while
regular tasks are placed in a lower-priority DSQ. Within each queue,
tasks are sorted based on their weighted runtime, using the built-in scx
vtime ordering capabilities (scx_bpf_dispatch_vtime()).
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).
Results
=======
According to the initial test results, using the same benchmark "playing
a videogame while recompiling the kernel", this scheduler seems to
provide a +5% improvement in the frames-per-second (fps) compared to
scx_rustland, with video games such as Cyberpunk 2077, Counter-Strike 2
and Baldur's Gate 3.
Initial test results indicate that this scheduler offers around a +5%
improvement in frames-per-second (fps) compared to scx_rustland when
using the benchmark "playing a video game while recompiling the kernel".
This improvement was observed in games such as Cyberpunk 2077,
Counter-Strike 2, and Baldur's Gate 3.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
2024-06-24 06:56:03 +01:00
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.
