DNM: microbench seastar urgent value/coroutine returns - #31613
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DNM: microbench seastar urgent value/coroutine returns#31613travisdowns wants to merge 1 commit into
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Pins seastar at travisdowns/seastar@2e6c9a1, which makes a continuation that returns a value - and a coroutine return - resume its waiter from the front of the reactor's task queue rather than the back. Not for merge; this exists to get a microbench comparison against the baseline.
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Performance change detected in https://buildkite.com/redpanda/redpanda/builds/88870#01a015bb-a728-4f25-a135-ca2989c25652: See https://redpandadata.atlassian.net/wiki/x/LQAqLg for docs |
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Do not merge. This exists only to get a
/microbenchcomparison against the baseline.Pins seastar at travisdowns/seastar@2e6c9a1 (branch
td-urgent-sched, cut fromv26.3.x), which addsset_value_urgent()and uses it from:futurize<T>::satisfy_with_result_of()coroutine_traits_base<T>::promise_type::return_value()/return_void()Today only the third branch of
satisfy_with_result_of()- the one where the continuation returns an already-ready future - resolves the next promise urgently, viaforward_to()->set_urgent_state(), which inserts the waiting task at the front of the reactor's task queue. The value and void branches callset_value(), which appends it to the back, behind everything queued while the chain was running. Coroutines always take the appending path, sincereturn_value()/return_void()go throughset_value(); withfinal_suspend()beingsuspend_never, each level of a nestedco_awaitchain resumes its caller from its own tail-inserted task.Note this changes the order in which queued tasks run. Seastar's
futures_testandcoroutines_testpass in dev, release and sanitize modes, and both files gain a test that asserts the new ordering.The point of the microbench run is that the change is otherwise unmeasured.