On 15/07/2020 23:09, Miklos Szeredi wrote: > On Wed, Jul 15, 2020 at 9:43 PM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: >> >> To clear details for those who are not familiar with io_uring: >> >> io_uring has a pair of queues, submission (SQ) and completion queues (CQ), >> both shared between kernel and user spaces. The userspace submits requests >> by filling a chunk of memory in SQ. The kernel picks up SQ entries in >> (syscall io_uring_enter) or asynchronously by polling SQ. >> >> CQ entries are filled by the kernel completely asynchronously and >> in parallel. Some users just poll CQ to get them, but also have a way >> to wait for them. >> >>>>> >>>>> What do people think? >>>>> >>>>> From what I can tell, listing the submitted requests on >>>>> io_uring_enter() would not be hard. Request completion is >>>>> asynchronous, however, and may not require io_uring_enter() syscall. >>>>> Am I correct? >> >> Both, submission and completion sides may not require a syscall. > > Okay. > >>>>> Is there some existing tracing infrastructure that strace could use to >>>>> get async completion events? Should we be introducing one? >> >> There are static trace points covering all needs. > > This needs to be unprivileged, or its usefulness is again compromized. > >> >> And if not used the whole thing have to be zero-overhead. Otherwise >> there is perf, which is zero-overhead, and this IMHO won't fly. > > Obviously it needs to be zero overhead if not tracing. > > What won't fly? Any approach that is not "zero-overhead if not used". -- Pavel Begunkov
