linux-kernel - Re: [PATCH v3 0/4] fast poll multishot mode

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Date:   Sat, 7 May 2022 22:06:04 +0800
From:   Hao Xu <haoxu.linux@...il.com>
To:     io-uring@...r.kernel.org
Cc:     Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/4] fast poll multishot mode

Something wrong with my git sendemail, trying to fix it. Please ignore 
this...

在 2022/5/7 下午8:38, Hao Xu 写道:
> 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
> 
> v2->v3:
>   - fold in code tweak and clean from Jens
>   - use io_issue_sqe rather than io_queue_sqe, since the former one
>     return the internal error back which makes more sense
>   - remove io_poll_clean() and its friends since they are not needed
> 
> 
> Hao Xu (4):
>    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
> 
>   fs/io_uring.c                 | 94 +++++++++++++++++++++++++++--------
>   include/uapi/linux/io_uring.h |  5 ++
>   2 files changed, 79 insertions(+), 20 deletions(-)
> 
> 
> base-commit: 0a194603ba7ee67b4e39ec0ee5cda70a356ea618