On Mon, 14 Jan 2019 19:55:20 -0700 Jens Axboe <axboe@xxxxxxxxx> wrote: So the [0/16] cover letter seems to have gone astray this time? Anyway, a couple of minor notes/questions: > The submission queue (SQ) and completion queue (CQ) rings are shared > between the application and the kernel. This eliminates the need to > copy data back and forth to submit and complete IO. > > IO submissions use the io_uring_sqe data structure, and completions > are generated in the form of io_uring_sqe data structures. The SQ > ring is an index into the io_uring_sqe array, which makes it possible > to submit a batch of IOs without them being contiguous in the ring. > The CQ ring is always contiguous, as completion events are inherently > unordered and can point to any io_uring_iocb. > > Two new system calls are added for this: > > io_uring_setup(entries, iovecs, params) > Sets up a context for doing async IO. On success, returns a file > descriptor that the application can mmap to gain access to the > SQ ring, CQ ring, and io_uring_iocbs. Looking at the code, it would appear that the "iovecs" parameter doesn't actually exist. > io_uring_enter(fd, to_submit, min_complete, flags) > Initiates IO against the rings mapped to this fd, or waits for > them to complete, or both The behavior is controlled by the > parameters passed in. If 'min_complete' is non-zero, then we'll > try and submit new IO. If IORING_ENTER_GETEVENTS is set, the > kernel will wait for 'min_complete' events, if they aren't > already available. I feel like I'm missing something here. Rather than have the IORING_ENTER_GETEVENTS flag, why not just wait if min_complete > 0 ? Thanks, jon
