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scx: Dispatch locally until ops.cpu_online() invoked #197
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htejun
approved these changes
May 3, 2024
In sched_ext, there's currently a corner case on the hotplug path wherein a CPU may be onlined and begin scheduling _before_ we've invoked ops.cpu_online() to the scheduler. This can cause confusion by e.g. causing a scheduler to error out if it receives an ops.dispatch() call and accidentally dispatches to an invalid DSQ. To avoid this scenario, this patch adds a per-CPU boolean variable that tracks when a CPU has been onlined from the perspective of sched_ext. Note that this patch does not prevent _any_ callback from being invoked on that CPU. It simply prevents us from invoking ops.dispatch(), and forces us to dispatch directly to the local DSQ. We can still, however, receive e.g. ops.runnable() if a per-CPU task is dispatched to the local DSQ of the onlined CPU before the hotplug event is received. Signed-off-by: David Vernet <[email protected]>
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In sched_ext, there's currently a corner case on the hotplug path wherein a CPU may be onlined and begin scheduling before we've invoked ops.cpu_online() to the scheduler. This can cause confusion by e.g. causing a scheduler to error out if it receives an ops.dispatch() call and accidentally dispatches to an invalid DSQ.
To avoid this scenario, this patch adds a per-CPU boolean variable that tracks when a CPU has been onlined from the perspective of sched_ext.
Note that this patch does not prevent any callback from being invoked on that CPU. It simply prevents us from invoking ops.dispatch(), and forces us to dispatch directly to the local DSQ. We can still, however, receive e.g. ops.runnable() if a per-CPU task is dispatched to the local DSQ of the onlined CPU before the hotplug event is received.