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    Subject[PATCH v2 0/5] fast poll multishot mode
    Date
    Let multishot support multishot mode, currently only add accept as its
    first comsumer.
    theoretical analysis:
    1) when connections come in fast
    - singleshot:
    add accept sqe(userpsace) --> accept inline
    ^ |
    |-----------------|
    - multishot:
    add accept sqe(userspace) --> accept inline
    ^ |
    |--*--|

    we do accept repeatedly in * place until get EAGAIN

    2) when connections come in at a low pressure
    similar thing like 1), we reduce a lot of userspace-kernel context
    switch and useless vfs_poll()


    tests:
    Did some tests, which goes in this way:

    server client(multiple)
    accept connect
    read write
    write read
    close close

    Basically, raise up a number of clients(on same machine with server) to
    connect to the server, and then write some data to it, the server will
    write those data back to the client after it receives them, and then
    close the connection after write return. Then the client will read the
    data and then close the connection. Here I test 10000 clients connect
    one server, data size 128 bytes. And each client has a go routine for
    it, so they come to the server in short time.
    test 20 times before/after this patchset, time spent:(unit cycle, which
    is the return value of clock())
    before:
    1930136+1940725+1907981+1947601+1923812+1928226+1911087+1905897+1941075
    +1934374+1906614+1912504+1949110+1908790+1909951+1941672+1969525+1934984
    +1934226+1914385)/20.0 = 1927633.75
    after:
    1858905+1917104+1895455+1963963+1892706+1889208+1874175+1904753+1874112
    +1874985+1882706+1884642+1864694+1906508+1916150+1924250+1869060+1889506
    +1871324+1940803)/20.0 = 1894750.45

    (1927633.75 - 1894750.45) / 1927633.75 = 1.65%


    A liburing test is here:
    https://github.com/HowHsu/liburing/blob/multishot_accept/test/accept.c

    v1->v2:
    - re-implement it against the reworked poll code

    Hao Xu (5):
    io_uring: add IORING_ACCEPT_MULTISHOT for accept
    io_uring: add REQ_F_APOLL_MULTISHOT for requests
    io_uring: let fast poll support multishot
    io_uring: add a helper for poll clean
    io_uring: implement multishot mode for accept

    fs/io_uring.c | 121 ++++++++++++++++++++++++++--------
    include/uapi/linux/io_uring.h | 5 ++
    2 files changed, 100 insertions(+), 26 deletions(-)


    base-commit: f2e030dd7aaea5a937a2547dc980fab418fbc5e7
    --
    2.36.0

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