Add hints to yield_now to allow schedulers to deprioritize a yielding thread
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jorajeev
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Apr 13, 2021
tests/asynch/pct.rs
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| asynch::block_on(async move { | ||
| while count.load(Ordering::SeqCst) < NUM_TASKS { | ||
| asynch::yield_now().await; |
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How about adding a variant of this test without the yield, showing that PCT finds the schedule where the test panics because we hit the max_steps limit?
jorajeev
reviewed
Apr 13, 2021
tests/basic/pct.rs
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| .collect::<Vec<_>>(); | ||
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| while count.load(Ordering::SeqCst) < NUM_THREADS { | ||
| thread::yield_now(); |
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Same as above -- add a variant of the test that panics without the yield?
jorajeev
reviewed
Apr 13, 2021
…ng thread Tasks that implement busy-wait loops or other infinite loops are a fairness issue for schedulers like PCT, which will run a thread indefinitely until it blocks. This change makes both sync and async versions of `yield_now` act as a hint to the scheduler that the current task should be deprioritized. Only the PCT scheduler acts on this hint, by moving the current task to the lowest priority. We could also make the DFS scheduler react to this hint by not allowing it to re-schedule the current task immediately, but that would be unsound.
jamesbornholt
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Good idea, done. |
jorajeev
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Apr 13, 2021
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Tasks that implement busy-wait loops or other infinite loops are a fairness
issue for schedulers like PCT, which will run a thread indefinitely until it
blocks. This change makes both sync and async versions of
yield_nowact asa hint to the scheduler that the current task should be deprioritized. Only
the PCT scheduler acts on this hint, by moving the current task to the lowest
priority. We could also make the DFS scheduler react to this hint by not
allowing it to re-schedule the current task immediately, but that would be
unsound.
By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.