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The current CPU selection logic in the scheduler presents some inefficiencies. When a task is drained from the BPF queue, the scheduler immediately checks whether the CPU previously assigned to the task is still idle, assigning it if it is. Otherwise, it iterates through available CPUs, always starting from CPU #0, and selects the first idle one without updating its state. This approach is consistently applied to the entire batch of tasks drained from the BPF queue, resulting in all of them being assigned to the same idle CPU (also with a higher likelihood of allocation to lower CPU ids rather than higher ones). While dispatching a batch of tasks to the same idle CPU is not necessarily problematic, a fairer distribution among the list of idle CPUs would be preferable. Therefore change the CPU selection logic to distribute tasks equally among the idle CPUs, still maintaining the preference for the previously used one. Additionally, apply the CPU selection logic just before tasks are dispatched, rather than assigning a CPU when tasks are drained from the BPF queue. This adjustment is important, because tasks may linger in the scheduler's internal structures for a bit and the idle state of the CPUs in the system may change during that period. Signed-off-by: Andrea Righi <andrea.righi@canonical.com> |
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| README.md | ||
| sync-to-kernel.sh | ||
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