eventfd 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.

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mananaysiempre 2 days ago | parent [-]

> 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

	▲	riyaneel 2 days ago \| parent [-]
		Fair point. The real difference is the narrower: with a futex the producer can inspect consumer_sleeping directly in shared memory and skip the FUTEX_WAKE entirely if the consumer is still spinning. With eventfd you need a write() regardless, or you add shared state to gate it, which is essentially rebuilding futex. Same idea but slightly less clean.