On 5/3/21 12:02 PM, Matthew Wilcox wrote: > 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. But then we really must get that fixed, imho ->read() and ->write() should go away, and if the iter variants are 10% slower, then that should get fixed up. I'll go over that thread. -- Jens Axboe
