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The current implementation of the user-space scheduler is strongly prioritizing newly created tasks by setting their initial vruntime to (min_vruntime + 1); this prioritization places them ahead of other tasks waiting to run. While this approach is efficient for processing short-lived tasks, it makes the scheduler vulnerable to fork-bomb attacks and significantly penalizes interactive workloads (e.g., "foreground" applications), in particular in the presence of background applications that are spawning multiple tasks, such as parallel builds. Instead of prioritizing newly created tasks, do the opposite and account (max_slice_ns / 2) to their initial vruntime, to make sure they are not scheduled before the other tasks that are already waiting for the CPU in the current scheduler run. This allows to mitigate potential fork-bomb attacks and it strongly improves the responsiveness of interactive applications (such as UI, audio/video streams, gaming, etc.). With this change applied, under certain conditions, scx_rustland can even outperform the default Linux scheduler. For example, with a parallel kernel build (make -j32) running in the background, I can play Terraria with a constant rate of ~30-40 fps, while the default Linux scheduler can handle only ~20-30 fps under the same conditions. Signed-off-by: Andrea Righi <andrea.righi@canonical.com> |
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SCHED_EXT SCHEDULERS
Introduction
This directory contains the repo's schedulers.
Some of these schedulers are simply examples of different types of schedulers that can be built using sched_ext. They can be loaded and used to schedule on your system, but their primary purpose is to illustrate how various features of sched_ext can be used.
Other schedulers are actually performant, production-ready schedulers. That is, for the correct workload and with the correct tuning, they may be deployed in a production environment with acceptable or possibly even improved performance. Some of the examples could be improved to become production schedulers.
Please see the following README files for details on each of the various types of schedulers:
- rust describes all of the schedulers with rust user space components. All of these schedulers are production ready.
- c describes all of the schedulers with C user space components. All of these schedulers are production ready.
Note on syncing
Note that there is a sync-to-kernel.sh script in this directory. This is used to sync any changes to the specific schedulers with the Linux kernel tree. If you've made any changes to a scheduler in please use the script to synchronize with the sched_ext Linux kernel tree:
$ ./sync-to-kernel.sh /path/to/kernel/tree