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Carl Lerche
9eb3f5b556
As an optimization to improve locality, the multi-threaded scheduler maintains a single slot (LIFO slot). When a task is scheduled, it goes into the LIFO slot. The scheduler will run tasks in the LIFO slot first before checking the local queue. Ping-ping style workloads where task A notifies task B, which notifies task A again, can cause starvation as these two tasks repeatedly schedule the other in the LIFO slot. #5686, a first attempt at solving this problem, consumes a unit of budget each time a task is scheduled from the LIFO slot. However, at the time of this commit, the scheduler allocates 128 units of budget for each chunk of work. This is relatively high in situations where tasks do not perform many async operations yet have meaningful poll times (even 5-10 microsecond poll times can have an outsized impact on the scheduler). In an ideal world, the scheduler would adapt to the workload it is executing. However, as a stopgap, this commit limits the times the LIFO slot is prioritized per scheduler tick.