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    SubjectRe: strace of io_uring events?
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    On 15/07/2020 23:09, Miklos Szeredi wrote:
    > On Wed, Jul 15, 2020 at 9:43 PM Pavel Begunkov <asml.silence@gmail.com> 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

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