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This ignores the existence of batching capabilities like epoll and io uring. Async IO may need to do more syscalls than blocking IO for a single operation, but the story looks different if you consider a large number of operations that are awaited as a group.

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io_uring actually changes this story because you can communicate events without crossing the syscall barrier, but only if you get enough incoming events to saturate your processing capabilities.

epoll batching only works in respect to the event notifications from kernel to user space. The only other thing that could be considered batched is that you can switch from "I want to read" to "I want to write" without telling the kernel first that you don't want to read anymore. But that's hardly worth mentioning.

It seems epoll could be slower than poll for async/await environments. It requires epoll_ctl (syscall) on each fd state transition. `poll` could wait in a single syscall for a small set of current blocked fds.

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