1fa7a5e697
Motivation: EPOLL supports decoupling the timed wakeup mechanism from the selector call. The EPOLL transport takes advantage of this in order to offer more fine grained timer resolution. However we are current calling timerfd_settime on each call to epoll_wait and this is expensive. We don't have to re-arm the timer on every call to epoll_wait and instead only have to arm the timer when a task is scheduled with an earlier expiration than any other existing scheduled task. Modifications: - Before scheduled tasks are added to the task queue, we determine if the new duration is the soonest to expire, and if so update with timerfd_settime. We also drain all the tasks at the end of the event loop to make sure we service any expired tasks and get an accurate next time delay. - EpollEventLoop maintains a volatile variable which represents the next deadline to expire. This variable is modified inside the event loop thread (before calling epoll_wait) and out side the event loop thread (immediately to ensure proper wakeup time). - Execute the task queue before the schedule task priority queue. This means we may delay the processing of scheduled tasks but it ensures we transfer all pending tasks from the task queue to the scheduled priority queue to run the soonest to expire scheduled task first. - Deprecate IORatio on EpollEventLoop, and drain the executor and scheduled queue on each event loop wakeup. Coupling the amount of time we are allowed to drain the executor queue to a proportion of time we process inbound IO may lead to unbounded queue sizes and unpredictable latency. Result: Fixes https://github.com/netty/netty/issues/7829 - In most cases this results in less calls to timerfd_settime - Less event loop wakeups just to check for scheduled tasks executed outside the event loop - More predictable executor queue and scheduled task queue draining - More accurate and responsive scheduled task execution |
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