Userland scheduler updates #63
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arighi
approved these changes
Jan 2, 2024
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Reviewed and tested, LGTM!
The fact that we start to have some duplicate code between the BPF part of scx_rustland and scx_userland makes me think if we should introduce at some point a common "BPF abstraction" to provide the basic APIs to implement the user-space schedulers... something to think about for the future.
htejun
reviewed
Jan 2, 2024
We can sometimes hit scenarios in the scx_userland scheduler where there is work to be done in user space, but we incorrectly fail to run the user space scheduler. In order to avoid this, we can use global variables that are set from both BPF and user space. The BPF-side variable reflects when one or more tasks have been enqueued, and the user space-side variable reflects when user space has received tasks but has not yet dispatched them. In the ops.update_idle() callback, we can check these variables and send a resched IPI to a core to ensure that the user-space scheduler is always scheduled when there's work to be done. Signed-off-by: David Vernet <void@manifault.com>
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This patch fixes a couple issues in the
scx_rustlandandscx_userlandscheduler:Inscx_rustland, we keep using builtin idle tracking withSCX_OPS_KEEP_BUILTIN_IDLEto avoid racy checks inops.select_cpu()scx_userland, we avoid hangs by using more robust checks to see if there's more work to be done in user space, and sending resched IPIs whenever there is.