Re: aio poll, io_pgetevents and a new in-kernel poll API V3

Jeff Moyer
2018-01-18T17:54:29Z

Avi Kivity <avi@scylladb.com> writes:

> On 01/18/2018 05:46 PM, Jeff Moyer wrote:
>> FYI, this kernel has issues. It will boot up, but I don't have
>> networking, and even rebooting doesn't succeed. I'm looking into it.
>
> FWIW, I'm running an older version of this patchset on my desktop with
> no problems so far.

Right, it's worth mentioning that v1 worked fine for me.

-Jeff

>> Christoph Hellwig <hch@lst.de> writes:
>>
>>> 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.3
>>>
>>> Gitweb:
>>>
>>> http://git.infradead.org/users/hch/vfs.git/shortlog/refs/heads/aio-poll.3
>>>
>>> Libaio changes:
>>>
>>> https://pagure.io/libaio.git io-poll
>>>
>>> Seastar changes (not updated for the new io_pgetevens ABI yet):
>>>
>>> https://github.com/avikivity/seastar/commits/aio
>>>
>>> Changes since V2:
>>> - removed a double initialization
>>> - new vfs_get_poll_head helper
>>> - document that ->get_poll_head can return NULL
>>> - call ->poll_mask before sleeping
>>> - various ACKs
>>> - add conversion of random to ->poll_mask
>>> - add conversion of af_alg to ->poll_mask
>>> - lacking ->poll_mask support now returns -EINVAL for IOCB_CMD_POLL
>>> - reshuffled the series so that prep patches and everything not
>>> requiring the new in-kernel poll API is in the beginning
>>>
>>> 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
>>>
>>> --
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>>> see: http://www.kvack.org/aio/
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>
>
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