On Mon, May 03, 2021 at 11:57:08AM -0600, Jens Axboe wrote: > On 5/3/21 10:12 AM, David Laight wrote: > > From: Jens Axboe > >> Sent: 03 May 2021 15:58 > >> > >> Had a report on writing to eventfd with io_uring is slower than it > >> should be, and it's the usual case of if a file type doesn't support > >> ->write_iter(), then io_uring cannot rely on IOCB_NOWAIT being honored > >> alongside O_NONBLOCK for whether or not this is a non-blocking write > >> attempt. That means io_uring will punt the operation to an io thread, > >> which will slow us down unnecessarily. > >> > >> Convert eventfd to using fops->write_iter() instead of fops->write(). > > > > Won't this have a measurable performance degradation on normal > > code that does write(event_fd, &one, 4); > > If ->write_iter() or ->read_iter() is much slower than the non-iov > versions, then I think we have generic issues that should be solved. We do! https://lore.kernel.org/linux-fsdevel/20210107151125.GB5270@xxxxxxxxxxxxxxxxxxxx/ is one thread on it. There have been others. > That should not be a consideration, since the non-iov ones are > legacy and should not be adopted in new code. > > -- > Jens Axboe >
