Hi, One thing that's always been a bit slower than I'd like with io_uring is dealing with pipes. They don't support IOCB_NOWAIT, and hence we need to punt them to io-wq for handling. This series adds support for FMODE_NOWAIT to pipes. Patch 1 extends pipe_buf_operations->confirm() to accept a nonblock parameter, and wires up the caller, pipe_buf_confirm(), to have that argument too. Patch 2 makes pipes deal with IOCB_NOWAIT for locking the pipe, calling pipe_buf_confirm(), and for allocating new pages on writes. Patch 3 flicks the switch and enables FMODE_NOWAIT for pipes. Curious on how big of a difference this makes, I wrote a small benchmark that simply opens 128 pipes and then does 256 rounds of reading and writing to them. This was run 10 times, discarding the first run as it's always a bit slower. Before the patch: Avg: 262.52 msec Stdev: 2.12 msec Min: 261.07 msec Max 267.91 msec and after the patch: Avg: 24.14 msec Stdev: 9.61 msec Min: 17.84 msec Max: 43.75 msec or about a 10x improvement in performance (and efficiency). I ran the patches through the ltp pipe and splice tests, no regressions observed. Looking at io_uring traces, we can see that we no longer have any io_uring_queue_async_work() traces after the patch, where previously everything was done via io-wq. -- Jens Axboe
