Re: [RFC 0/6] fast poll multishot mode

[Hao Xu <haoxu@linux.alibaba.com>]

在 2021/9/3 下午7:00, Hao Xu 写道:
> Let multishot support multishot mode, currently only add accept as its

               ^ fast poll
> 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%
> 
> Higher pressure like 10^5 connections causes problems since ports are
> in use.
> I'll test the cancellation path and try to lift pressure to much high
> level to see if numbers get better. Sent this early for comments and
> suggestions.
> 
> Hao Xu (6):
>    io_uring: enhance flush completion logic
>    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: implement multishot mode for accept
>    io_uring: enable multishot mode for accept
> 
>   fs/io_uring.c                 | 72 +++++++++++++++++++++++++++++------
>   include/uapi/linux/io_uring.h |  4 ++
>   2 files changed, 64 insertions(+), 12 deletions(-)
>