scx_rustland_core: prevent CI failures #662
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Updating nr_queued in a non-atomic when a queued task is consumed can lead to underflows. We don't really care about being 100% accurate here, since nr_queued should be considered more of a statistic than an accurate value. Therefore, just accept the fact that nr_queued can be inaccurate and handle potential underflows. Signed-off-by: Andrea Righi <[email protected]>
Dispatching kthreads via user-space can still lead to deadlocks in certain cases (for example we can still trigger stalls by running the fork stressor via stress-ng). To prevent such stalls simply dispatch kthreads directly from BPF for now to prevent failures. In the future we may consider to provide an API to restrict the selection of tasks directly dispatched (for example passing a mask PF_* flags to "whitelist" the tasks that are allowed to bypass the user-space scheduler). Signed-off-by: Andrea Righi <[email protected]>
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Merging to see if we can reduce the amount of failures with CI. |
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I think we want those failures. I haven't looked a to at how stress-ng is being called in the tests, but like, stress-ng is stalling which doesn't make the tests fail like kernel threads stalling does, but the tests should still fail (they're passing with stalls atm): https://github.com/sched-ext/scx/actions/runs/10936241301/job/30359538896#step:16:363 |
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meh ok... it's still failing then, I really don't understand what's going on with the stress-ng fork stressor, it really breaks rustland badly... I will investigate more. |
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A couple of changes that should finally prevent all the CI failures.
With this applied, the schedulers based on scx_rustland_core will always dispatch kthreads directly from the BPF component. This should be a safer option for now, allowing to prevent potential stalls also under heavy stress test conditions.
In the future, we will provide a better API to enforce stricter selection criteria for tasks permitted to bypass user-space scheduling.