rt: make the LIFO slot in the multi-threaded scheduler stealable #4941
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A-tokio
Area: The main tokio crate
C-feature-request
Category: A feature request.
M-runtime
Module: tokio/runtime
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carllerche
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Aug 24, 2022
The multi-threaded scheduler includes a per-worker LIFO slot to store the last scheduled task. This can improve certain usage patterns, especially message passing between tasks. However, this LIFO slot is not currently stealable. Eventually, the LIFO slot **will** become stealable. However, as a stop-gap, this unstable option lets users disable the LIFO task when doing so improves their application's overall performance. Refs: #4941
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Is there any further information available on this? I seem to have hit some pathological worst-case behavior with very cpu-heavy tasks, where every thread except one ended up totally stalled. Disabling the LIFO slot resolved the problem, giving me a 20x speedup. |
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It has not been implemented yet. |
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Should we make a counter that tracks times when if possible, the lifo slot would have been stolen? This could help application authors know if they should try the mitigation. |
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The multi-threaded scheduler includes a per-worker LIFO slot used to store the last scheduled task. This can improve certain usage patterns, especially message passing between tasks. However, this LIFO slot is not currently stealable.
As a temporary workaround, #4936 adds an unstable configuration option to disable the LIFO slot.
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