> Waking up "Thread B" was completely unnecessary and wastes precious resources. Epoll in level-triggered mode scales out poorly.
In the analysed situation thread B was already in a wait state and there aren't enough incoming connections to immediately accept the next one. Of course the resources (CPU time) were wasted, but does that impact the performance in any way? (Assuming one "main" application on that host)
Because the time wasted by all the threads trying to accept() or read() on the ready socket introduces latency for all other sockets. And since throughput is bounded by the number of threads divided by inverse of latency, increasing the latency makes you lose in scalability.
In addition, because a single "readiness event" has to wake up many threads, it can introduce lock contention and cacheline bouncing in the kernel's data structures.
> Waking up "Thread B" was completely unnecessary and wastes precious resources. Epoll in level-triggered mode scales out poorly.
In the analysed situation thread B was already in a wait state and there aren't enough incoming connections to immediately accept the next one. Of course the resources (CPU time) were wasted, but does that impact the performance in any way? (Assuming one "main" application on that host)