Andrea Righi 2cd3929475 scx_rustland: mitigate sub-optimal performance with offline CPUs ... Most of the schedulers assume that the amount of possible CPUs in the system represents the actual number of CPUs available. This is not always true: some CPUs may be offline or certain CPU models (AMD CPUs for example) may include unavailable CPUs in this number. This can lead to sub-optimal performance or even errors in the scheduler (see for example [1][2]). Ideally, we need to attack this issue in a more generic way, such as having a proper API provided by a C library, that can be used by all schedulers and the topology Rust module (scx_utils crate). But for now, let's try to mitigate most of the common sub-optimal cases separately inside each scheduler. For rustland we can apply some mitigations both in select_cpu() (for the BPF part) and in the user-space part: - the former is fixed in the sched-ext kernel by commit 94dc0c01b957 ("scx: Use cpu_online_mask when resetting idle masks"). However, adding an extra check `cpu < num_possible_cpus` in select_cpu(), allows to properly support AMD CPUs, even with kernels that don't have the cpu_online_mask fix yet (this doesn't always guarantee the validity of cpu, but it should be enough to mitigate the majority of the potential sub-optimal cases, without introducing any significant overhead) - the latter can be fixed relying on topology.span(), instead of topology.nr_cpus(), to count the amount of available CPUs in the system. [1] https://github.com/sched-ext/sched_ext/issues/69 [2] https://github.com/sched-ext/scx/issues/147 Link: 94dc0c01b9 Signed-off-by: Andrea Righi <andrea.righi@canonical.com>		2024-03-14 10:19:31 +01:00
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scx_rustland_core	scx_rustland: mitigate sub-optimal performance with offline CPUs	2024-03-14 10:19:31 +01:00
scx_utils	Merge pull request #178 from sched-ext/multi_numa_rusty	2024-03-12 15:50:27 -05:00
meson.build	rust: introduce scx_rustland_core crate	2024-02-28 17:49:44 +01:00