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

[Christoph Hellwig]

And of coure I should have added linux-api to the series.

Note that the libaio patches include documenting io_pgetevents in the
io_getevents man page.

On Thu, Jan 04, 2018 at 09:00:12AM +0100, 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
> 
> Libaio changes:
> 
>     http://git.infradead.org/users/hch/libaio.git/shortlog/refs/heads/aio-poll
> 
> Seastar changes:
> 
>     https://github.com/avikivity/seastar/commits/aio
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