From: Jens Axboe > Sent: 25 June 2021 01:45 > > On 6/22/21 6:17 AM, Olivier Langlois wrote: > > It is quite frequent that when an operation fails and returns EAGAIN, > > the data becomes available between that failure and the call to > > vfs_poll() done by io_arm_poll_handler(). > > > > Detecting the situation and reissuing the operation is much faster > > than going ahead and push the operation to the io-wq. > > > > Performance improvement testing has been performed with: > > Single thread, 1 TCP connection receiving a 5 Mbps stream, no sqpoll. > > > > 4 measurements have been taken: > > 1. The time it takes to process a read request when data is already available > > 2. The time it takes to process by calling twice io_issue_sqe() after vfs_poll() indicated that data > was available > > 3. The time it takes to execute io_queue_async_work() > > 4. The time it takes to complete a read request asynchronously > > > > 2.25% of all the read operations did use the new path. How much slower is it when the data to complete the read isn't available? I suspect there are different workflows where that is almost always true. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
