linux-kernel - Re: aio poll, io_pgetevents and a new in-kernel poll API V2

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Message-ID: <7eda0558-dc70-2d0c-5eca-ca4c3036585d@gmail.com>
Date:   Wed, 10 Jan 2018 23:36:19 +0100
From:   "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:     Christoph Hellwig <hch@....de>, viro@...iv.linux.org.uk
Cc:     mtk.manpages@...il.com, Avi Kivity <avi@...lladb.com>,
        linux-aio@...ck.org, linux-fsdevel@...r.kernel.org,
        netdev@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: aio poll, io_pgetevents and a new in-kernel poll API V2

Hi Christoph,

On 01/10/2018 04:58 PM, Christoph Hellwig wrote:
> Hi all,
> 
> this series adds support for the IOCB_CMD_POLL operation to poll for the
> readyness of file descriptors using the aio subsystem.  The API is based
> on patches that existed in RHAS2.1 and RHEL3, which means it already is
> supported by libaio.  To implement the poll support efficiently new
> methods to poll are introduced in struct file_operations:  get_poll_head
> and poll_mask.  The first one returns a wait_queue_head to wait on
> (lifetime is bound by the file), and the second does a non-blocking
> check for the POLL* events.  This allows aio poll to work without
> any additional context switches, unlike epoll.
> 
> To make the interface fully useful a new io_pgetevents system call is
> added, which atomically saves and restores the signal mask over the
> io_pgetevents system call.  It it the logical equivalent to pselect and
> ppoll for io_pgetevents.
> 
> The corresponding libaio changes for io_pgetevents support and
> documentation, as well as a test case will be posted in a separate
> series.
> 
> The changes were sponsored by Scylladb, and improve performance
> of the seastar framework up to 10%, while also removing the need
> for a privileged SCHED_FIFO epoll listener thread.
> 
> The patches are on top of Als __poll_t annoations, so I've also
> prepared a git branch on top of those here:
> 
>     git://git.infradead.org/users/hch/vfs.git aio-poll
> 
> Gitweb:
> 
>     http://git.infradead.org/users/hch/vfs.git/shortlog/refs/heads/aio-poll.2
> 
> Libaio changes:
> 
>     http://git.infradead.org/users/hch/libaio.git/shortlog/refs/heads/aio-poll
> 
> Seastar changes:
> 
>     https://github.com/avikivity/seastar/commits/aio
> 
> Changes since V1:
>  - handle the NULL ->poll case in vfs_poll
>  - dropped the file argument to the ->poll_mask socket operation
>  - replace the ->pre_poll socket operation with ->get_poll_head as
>    in the file operations

Are there some man pages patches already for these changes?

Thanks,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/