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io_uring: multishot recv

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Support multishot receive for io_uring.
Typical server applications will run a loop where for each recv CQE it
requeues another recv/recvmsg.

This can be simplified by using the existing multishot functionality
combined with io_uring's provided buffers.
The API is to add the IORING_RECV_MULTISHOT flag to the SQE. CQEs will
then be posted (with IORING_CQE_F_MORE flag set) when data is available
and is read. Once an error occurs or the socket ends, the multishot will
be removed and a completion without IORING_CQE_F_MORE will be posted.

The benefit to this is that the recv is much more performant.
 * Subsequent receives are queued up straight away without requiring the
   application to finish a processing loop.
 * If there are more data in the socket (sat the provided buffer size is
   smaller than the socket buffer) then the data is immediately
   returned, improving batching.
 * Poll is only armed once and reused, saving CPU cycles

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220630091231.1456789-11-dylany@fb.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dylan Yudaken
2022-06-30 02:12:29 -07:00
committed by Jens Axboe
parent cbd2574854
commit b3fdea6ecb
2 changed files with 94 additions and 13 deletions
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5
include/uapi/linux/io_uring.h
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@@ -263,8 +263,13 @@ enum io_uring_op {
* or receive and arm poll if that yields an
* -EAGAIN result, arm poll upfront and skip
* the initial transfer attempt.
*
* IORING_RECV_MULTISHOT Multishot recv. Sets IORING_CQE_F_MORE if
* the handler will continue to report
* CQEs on behalf of the same SQE.
*/
#define IORING_RECVSEND_POLL_FIRST (1U << 0)
#define IORING_RECV_MULTISHOT (1U << 1)
/*
* accept flags stored in sqe->ioprio