Commit e307e669 authored by Stefan Metzmacher's avatar Stefan Metzmacher Committed by Jens Axboe
Browse files

io_uring/net: introduce IORING_SEND_ZC_REPORT_USAGE flag 

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: default avatarStefan Metzmacher <metze@samba.org>
Reviewed-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8945b01756d902f5d5b0667f20b957ad3f742e5e.1666895626.git.metze@samba.org


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent eb708140

include/uapi/linux/io_uring.h

+18 −0
Original line number Diff line number Diff line
@@ -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

io_uring/net.c

+5 −1
Original line number Diff line number Diff line
@@ -937,7 +937,8 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) 


	zc->flags = READ_ONCE(sqe->ioprio);

	if (zc->flags & ~(IORING_RECVSEND_POLL_FIRST |

			  IORING_RECVSEND_FIXED_BUF))

			  IORING_RECVSEND_FIXED_BUF |

			  IORING_SEND_ZC_REPORT_USAGE))

		return -EINVAL;

	notif = zc->notif = io_alloc_notif(ctx);

	if (!notif)
@@ -955,6 +956,9 @@ int io_send_zc_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe) 
		req->imu = READ_ONCE(ctx->user_bufs[idx]);

		io_req_set_rsrc_node(notif, ctx, 0);

	}

	if (zc->flags & IORING_SEND_ZC_REPORT_USAGE) {

		io_notif_to_data(notif)->zc_report = true;

	}



	if (req->opcode == IORING_OP_SEND_ZC) {

		if (READ_ONCE(sqe->__pad3[0]))

io_uring/notif.c

+12 −0
Original line number Diff line number Diff line
@@ -18,6 +18,10 @@ static void __io_notif_complete_tw(struct io_kiocb *notif, bool *locked) 
		__io_unaccount_mem(ctx->user, nd->account_pages);

		nd->account_pages = 0;

	}



	if (nd->zc_report && (nd->zc_copied || !nd->zc_used))

		notif->cqe.res |= IORING_NOTIF_USAGE_ZC_COPIED;



	io_req_task_complete(notif, locked);

}
@@ -28,6 +32,13 @@ static void io_uring_tx_zerocopy_callback(struct sk_buff *skb, 
	struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);

	struct io_kiocb *notif = cmd_to_io_kiocb(nd);



	if (nd->zc_report) {

		if (success && !nd->zc_used && skb)

			WRITE_ONCE(nd->zc_used, true);

		else if (!success && !nd->zc_copied)

			WRITE_ONCE(nd->zc_copied, true);

	}



	if (refcount_dec_and_test(&uarg->refcnt)) {

		notif->io_task_work.func = __io_notif_complete_tw;

		io_req_task_work_add(notif);
@@ -55,6 +66,7 @@ struct io_kiocb *io_alloc_notif(struct io_ring_ctx *ctx) 
	nd->account_pages = 0;

	nd->uarg.flags = SKBFL_ZEROCOPY_FRAG | SKBFL_DONT_ORPHAN;

	nd->uarg.callback = io_uring_tx_zerocopy_callback;

	nd->zc_report = nd->zc_used = nd->zc_copied = false;

	refcount_set(&nd->uarg.refcnt, 1);

	return notif;

}

io_uring/notif.h

+3 −0
Original line number Diff line number Diff line
@@ -13,6 +13,9 @@ struct io_notif_data { 
	struct file		*file;

	struct ubuf_info	uarg;

	unsigned long		account_pages;

	bool			zc_report;

	bool			zc_used;

	bool			zc_copied;

};



void io_notif_flush(struct io_kiocb *notif);