Re: IORING_OP_POLL_ADD slower than linux-aio IOCB_CMD_POLL

[Jens Axboe <axboe@kernel.dk>]

On 4/19/22 5:07 AM, Avi Kivity wrote:
> A simple webserver shows about 5% loss compared to linux-aio.
> 
> 
> I expect the loss is due to an optimization that io_uring lacks -
> inline completion vs workqueue completion:

I don't think that's it, io_uring never punts to a workqueue for
completions. The aio inline completions is more of a hack because it
needs to do that, as always using a workqueue would lead to bad
performance and higher overhead.

So if there's a difference in performance, it's something else and we
need to look at that. But your report is pretty lacking! What kernel are
you running?

Do you have a test case of sorts?

For a performance oriented network setup, I'd normally not consider data
readiness poll replacements to be that interesting, my recommendation
would be to use async send/recv for that instead. That's how io_uring is
supposed to be used, in a completion based model.

-- 
Jens Axboe