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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
View file

@ -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

6
io_uring/net.c
View file

@ -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]))

12
io_uring/notif.c
View file

@ -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;
}

3
io_uring/notif.h
View file

@ -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);