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: 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>

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 2df3225b562fa4d4db4cc3ed1e8d08d16cf50454..9d4c4078e8d00e23957314892bf5963b938220db 100644 (file)
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -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

diff --git a/io_uring/net.c b/io_uring/net.c
index ab83da7e80f041f0001e5c8376ffaf521b1c2aac..03825b043afe1aaaa023d7dbe01ce83689e9ee02 100644 (file)
--- a/io_uring/net.c
+++ b/io_uring/net.c
@@ -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]))

diff --git a/io_uring/notif.c b/io_uring/notif.c
index e37c6569d82e8da251357e9e30105757037a0b9e..4bfef10161fa01e6e9f8bc68529d48607f15c3a7 100644 (file)
--- a/io_uring/notif.c
+++ b/io_uring/notif.c
@@ -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;
 }

diff --git a/io_uring/notif.h b/io_uring/notif.h
index 5b4d710c8ca541bcb572dcef330ac16adec19d34..4ae696273c781a125c20a3e5f03ad4b9ae84b17e 100644 (file)
--- a/io_uring/notif.h
+++ b/io_uring/notif.h
@@ -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);