From Christoph Hellwig <> Subject aio poll, io_pgetevents and a new in-kernel poll API Date Thu, 4 Jan 2018 09:00:12 +0100 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



