I've started working on adding SO_PREFER_BUSY_POLL [1] to afxdp-rs [2]. I have a few questions that I haven't been able to answer definitively from docs or commits. 1) To confirm, configuration like the below is required? echo 2 | sudo tee /sys/class/net/ens785f1/napi_defer_hard_irqs echo 200000 | sudo tee /sys/class/net/ens785f1/gro_flush_timeout 2) It's not clear to me what polling operations are required. It looks like the xdpdock example was modified to call recvfrom() and sendto() in every situation where previously the condition was that the need_wakeup flag was set on one of the queues. It looks like this structure may do extra syscalls? It it sufficient to 'poll' (I don't mean the syscall here) the socket once with one syscall operation or do we need the equivalent of a send and recv operation (like the example) in each loop iteration? 3) The patch linked below mentions adding recvmsg and sendmsg support for busy polling. The xdpsock example uses recvfrom(). What is the set of syscalls that can drive the busy polling? Is there a recommendation for which one(s) should be used? 4) In situations where there are multiple sockets, will it work to do one poll syscall with multiple fds to reduce the number of syscalls? Is that a good idea? 5) "If the application stops performing busy-polling via a system call, the watchdog timer defined by gro_flush_timeout will timeout, and regular softirq handling will resume." Does this imply that if the application fails to poll within the watchdog time that it needs to take action to get back into prefer busy polling mode? On the plus side, the initial performance numbers look good but there are a lot of drops as traffic ramps up that I haven't figured out the cause of yet. There are no drops once it's running in a steady state. Thanks for any help or insight. [1] - https://lwn.net/Articles/837010/ [2] - https://github.com/aterlo/afxdp-rs
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