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scx_rustland: prevent dispatching multiple tasks on the same idle cpu #58

Merged
merged 1 commit into from
Dec 31, 2023
Merged

scx_rustland: prevent dispatching multiple tasks on the same idle cpu #58

merged 1 commit into from
Dec 31, 2023

Commits on Dec 31, 2023

  1. scx_rustland: prevent dispatching multiple tasks on the same idle cpu 

    When a task is dispatched we always try to pick the previously used CPU
(if idle) to minimize the migration overhead. Alternatively, if such CPU
is not available, we pick any other idle CPU in the system.

However, we don't update the list of idle CPUs as we dispatch tasks,
therefore we may end up sending multiple tasks to the same idle CPU (if
their previously used CPU is the same) and we may even skip some idle
CPUs completely.

Change this logic to make sure that we never dispatch multiple tasks to
the same idle CPU, by updating the list of idle CPUs as we send tasks to
the BPF dispatcher.

This also avoids dispatching tasks with a closely matched vruntime to
the same CPU, thereby negating the advantages of the vruntime ordering.
With this change in place, we ensure that tasks with a similar vruntime
are dispatched to different CPUs, leading to significant improvements in
latency performance.

Signed-off-by: Andrea Righi <[email protected]>
    Andrea Righi committed Dec 31, 2023
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