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io_uring/net: introduce IORING_SEND_ZC_REPORT_USAGE flag

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It might be useful for applications to detect if a zero copy transfer with
SEND[MSG]_ZC was actually possible or not. The application can fallback to
plain SEND[MSG] in order to avoid the overhead of two cqes per request. Or
it can generate a log message that could indicate to an administrator that
no zero copy was possible and could explain degraded performance.

Cc: stable@vger.kernel.org # 6.1
Link: https://lore.kernel.org/io-uring/fb6a7599-8a9b-15e5-9b64-6cd9d01c6ff4@gmail.com/T/#m2b0d9df94ce43b0e69e6c089bdff0ce6babbdfaa
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8945b01756d902f5d5b0667f20b957ad3f742e5e.1666895626.git.metze@samba.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Stefan Metzmacher
2022-10-27 20:34:45 +02:00
committed by Jens Axboe
parent eb7081409f
commit e307e66981
4 changed files with 38 additions and 1 deletions
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18
include/uapi/linux/io_uring.h
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@@ -296,10 +296,28 @@ enum io_uring_op {
*
* IORING_RECVSEND_FIXED_BUF Use registered buffers, the index is stored in
* the buf_index field.
*
* IORING_SEND_ZC_REPORT_USAGE
* If set, SEND[MSG]_ZC should report
* the zerocopy usage in cqe.res
* for the IORING_CQE_F_NOTIF cqe.
* 0 is reported if zerocopy was actually possible.
* IORING_NOTIF_USAGE_ZC_COPIED if data was copied
* (at least partially).
*/
#define IORING_RECVSEND_POLL_FIRST (1U << 0)
#define IORING_RECV_MULTISHOT (1U << 1)
#define IORING_RECVSEND_FIXED_BUF (1U << 2)
#define IORING_SEND_ZC_REPORT_USAGE (1U << 3)
/*
* cqe.res for IORING_CQE_F_NOTIF if
* IORING_SEND_ZC_REPORT_USAGE was requested
*
* It should be treated as a flag, all other
* bits of cqe.res should be treated as reserved!
*/
#define IORING_NOTIF_USAGE_ZC_COPIED (1U << 31)
/*
* accept flags stored in sqe->ioprio