On Fri, 2021-06-25 at 08:15 +0000, David Laight wrote: > 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, in the case that the data to complete isn't available, the request will be processed exactly as it was before the patch. Ideally through io_uring fast polling feature. If not possible because arming the poll has been aborted, the request will be punted to the io- wq. Greetings,
