alt Hacker Newseventfd always pays a syscall on both sides (~200-400ns) regardless of load. Tachyon slow path only kick in under genuine starvation: the consumer spins first, then FUTEX_WAIT, and the producer skips FUTEX_WAKE entirely if the consumer still spinning. At sustainable rates the slow path never activates.
> eventfd always pays a syscall on both sides (~200-400ns) regardless of load.
It’s fairly standard to make the waiting side spin a bit after processing some data, and only issue another wait syscall if no more data arrives during the spin period.
(For instance, io_uring, which does this kind of IPC with a kernel thread on the receiving side, literally lets you configure how long said kernel thread should spin[1].)
[1] https://unixism.net/loti/tutorial/sq_poll.html