Merge branch 'for-uring-ubufops' into HEAD

Pavel Begunkov says:

====================
implement io_uring notification (ubuf_info) stacking (net part)

To have per request buffer notifications each zerocopy io_uring send
request allocates a new ubuf_info. However, as an skb can carry only
one uarg, it may force the stack to create many small skbs hurting
performance in many ways.

The patchset implements notification, i.e. an io_uring's ubuf_info
extension, stacking. It attempts to link ubuf_info's into a list,
allowing to have multiple of them per skb.

liburing/examples/send-zerocopy shows up 6 times performance improvement
for TCP with 4KB bytes per send, and levels it with MSG_ZEROCOPY. Without
the patchset it requires much larger sends to utilise all potential.

bytes | before | after (Kqps)
1200 | 195 | 1023
4000 | 193 | 1386
8000 | 154 | 1058
====================

Link: https://lore.kernel.org/all/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/tap.c

···
 		skb_zcopy_init(skb, msg_control);
 	} else if (msg_control) {
 		struct ubuf_info *uarg = msg_control;
-		uarg->callback(NULL, uarg, false);
+		uarg->ops->complete(NULL, uarg, false);
 	}
 
 	dev_queue_xmit(skb);

drivers/net/tun.c

···
 		skb_zcopy_init(skb, msg_control);
 	} else if (msg_control) {
 		struct ubuf_info *uarg = msg_control;
-		uarg->callback(NULL, uarg, false);
+		uarg->ops->complete(NULL, uarg, false);
 	}
 
 	skb_reset_network_header(skb);

drivers/net/xen-netback/common.h

···
 
 void xenvif_carrier_on(struct xenvif *vif);
 
-/* Callback from stack when TX packet can be released */
-void xenvif_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *ubuf,
-			      bool zerocopy_success);
+/* Callbacks from stack when TX packet can be released */
+extern const struct ubuf_info_ops xenvif_ubuf_ops;
 
 static inline pending_ring_idx_t nr_pending_reqs(struct xenvif_queue *queue)
 {

drivers/net/xen-netback/interface.c

···
 
 	for (i = 0; i < MAX_PENDING_REQS; i++) {
 		queue->pending_tx_info[i].callback_struct = (struct ubuf_info_msgzc)
-			{ { .callback = xenvif_zerocopy_callback },
+			{ { .ops = &xenvif_ubuf_ops },
 			  { { .ctx = NULL,
 			      .desc = i } } };
 		queue->grant_tx_handle[i] = NETBACK_INVALID_HANDLE;

drivers/net/xen-netback/netback.c

···
 	uarg = skb_shinfo(skb)->destructor_arg;
 	/* increase inflight counter to offset decrement in callback */
 	atomic_inc(&queue->inflight_packets);
-	uarg->callback(NULL, uarg, true);
+	uarg->ops->complete(NULL, uarg, true);
 	skb_shinfo(skb)->destructor_arg = NULL;
 
 	/* Fill the skb with the new (local) frags. */
···
 	return work_done;
 }
 
-void xenvif_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *ubuf_base,
-			      bool zerocopy_success)
+static void xenvif_zerocopy_callback(struct sk_buff *skb,
+				     struct ubuf_info *ubuf_base,
+				     bool zerocopy_success)
 {
 	unsigned long flags;
 	pending_ring_idx_t index;
···
 		queue->stats.tx_zerocopy_fail++;
 	xenvif_skb_zerocopy_complete(queue);
 }
+
+const struct ubuf_info_ops xenvif_ubuf_ops = {
+	.complete = xenvif_zerocopy_callback,
+};
 
 static inline void xenvif_tx_dealloc_action(struct xenvif_queue *queue)
 {

drivers/vhost/net.c

···
 	}
 }
 
-static void vhost_zerocopy_callback(struct sk_buff *skb,
+static void vhost_zerocopy_complete(struct sk_buff *skb,
 				    struct ubuf_info *ubuf_base, bool success)
 {
 	struct ubuf_info_msgzc *ubuf = uarg_to_msgzc(ubuf_base);
···
 
 	rcu_read_unlock_bh();
 }
+
+static const struct ubuf_info_ops vhost_ubuf_ops = {
+	.complete = vhost_zerocopy_complete,
+};
 
 static inline unsigned long busy_clock(void)
 {
···
 			vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
 			ubuf->ctx = nvq->ubufs;
 			ubuf->desc = nvq->upend_idx;
-			ubuf->ubuf.callback = vhost_zerocopy_callback;
+			ubuf->ubuf.ops = &vhost_ubuf_ops;
 			ubuf->ubuf.flags = SKBFL_ZEROCOPY_FRAG;
 			refcount_set(&ubuf->ubuf.refcnt, 1);
 			msg.msg_control = &ctl;

include/linux/skbuff.h

···
 #define SKBFL_ALL_ZEROCOPY	(SKBFL_ZEROCOPY_FRAG | SKBFL_PURE_ZEROCOPY | \
 				 SKBFL_DONT_ORPHAN | SKBFL_MANAGED_FRAG_REFS)
 
+struct ubuf_info_ops {
+	void (*complete)(struct sk_buff *, struct ubuf_info *,
+			 bool zerocopy_success);
+	/* has to be compatible with skb_zcopy_set() */
+	int (*link_skb)(struct sk_buff *skb, struct ubuf_info *uarg);
+};
+
 /*
  * The callback notifies userspace to release buffers when skb DMA is done in
  * lower device, the skb last reference should be 0 when calling this.
···
  * The desc field is used to track userspace buffer index.
  */
 struct ubuf_info {
-	void (*callback)(struct sk_buff *, struct ubuf_info *,
-			 bool zerocopy_success);
+	const struct ubuf_info_ops *ops;
 	refcount_t refcnt;
 	u8 flags;
 };
···
 }
 #endif
 
+extern const struct ubuf_info_ops msg_zerocopy_ubuf_ops;
+
 struct ubuf_info *msg_zerocopy_realloc(struct sock *sk, size_t size,
 				       struct ubuf_info *uarg);
 
 void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref);
-
-void msg_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *uarg,
-			   bool success);
 
 int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk,
 			    struct sk_buff *skb, struct iov_iter *from,
···
 static inline void net_zcopy_put(struct ubuf_info *uarg)
 {
 	if (uarg)
-		uarg->callback(NULL, uarg, true);
+		uarg->ops->complete(NULL, uarg, true);
 }
 
 static inline void net_zcopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 {
 	if (uarg) {
-		if (uarg->callback == msg_zerocopy_callback)
+		if (uarg->ops == &msg_zerocopy_ubuf_ops)
 			msg_zerocopy_put_abort(uarg, have_uref);
 		else if (have_uref)
 			net_zcopy_put(uarg);
···
 
 	if (uarg) {
 		if (!skb_zcopy_is_nouarg(skb))
-			uarg->callback(skb, uarg, zerocopy_success);
+			uarg->ops->complete(skb, uarg, zerocopy_success);
 
 		skb_shinfo(skb)->flags &= ~SKBFL_ALL_ZEROCOPY;
 	}

io_uring/notif.c

···
 	io_req_task_complete(notif, ts);
 }
 
-static void io_tx_ubuf_callback(struct sk_buff *skb, struct ubuf_info *uarg,
+static void io_tx_ubuf_complete(struct sk_buff *skb, struct ubuf_info *uarg,
 				bool success)
 {
 	struct io_notif_data *nd = container_of(uarg, struct io_notif_data, uarg);
···
 		else if (!success && !nd->zc_copied)
 			WRITE_ONCE(nd->zc_copied, true);
 	}
-	io_tx_ubuf_callback(skb, uarg, success);
+	io_tx_ubuf_complete(skb, uarg, success);
 }
+
+static const struct ubuf_info_ops io_ubuf_ops = {
+	.complete = io_tx_ubuf_complete,
+};
+
+static const struct ubuf_info_ops io_ubuf_ops_ext = {
+	.complete = io_tx_ubuf_callback_ext,
+};
 
 void io_notif_set_extended(struct io_kiocb *notif)
 {
 	struct io_notif_data *nd = io_notif_to_data(notif);
 
-	if (nd->uarg.callback != io_tx_ubuf_callback_ext) {
+	if (nd->uarg.ops != &io_ubuf_ops_ext) {
 		nd->account_pages = 0;
 		nd->zc_report = false;
 		nd->zc_used = false;
 		nd->zc_copied = false;
-		nd->uarg.callback = io_tx_ubuf_callback_ext;
+		nd->uarg.ops = &io_ubuf_ops_ext;
 		notif->io_task_work.func = io_notif_complete_tw_ext;
 	}
 }
···
 
 	nd = io_notif_to_data(notif);
 	nd->uarg.flags = IO_NOTIF_UBUF_FLAGS;
-	nd->uarg.callback = io_tx_ubuf_callback;
+	nd->uarg.ops = &io_ubuf_ops;
 	refcount_set(&nd->uarg.refcnt, 1);
 	return notif;
 }

net/core/skbuff.c

···
 		return NULL;
 	}
 
-	uarg->ubuf.callback = msg_zerocopy_callback;
+	uarg->ubuf.ops = &msg_zerocopy_ubuf_ops;
 	uarg->id = ((u32)atomic_inc_return(&sk->sk_zckey)) - 1;
 	uarg->len = 1;
 	uarg->bytelen = size;
···
 		u32 bytelen, next;
 
 		/* there might be non MSG_ZEROCOPY users */
-		if (uarg->callback != msg_zerocopy_callback)
+		if (uarg->ops != &msg_zerocopy_ubuf_ops)
 			return NULL;
 
 		/* realloc only when socket is locked (TCP, UDP cork),
···
 	sock_put(sk);
 }
 
-void msg_zerocopy_callback(struct sk_buff *skb, struct ubuf_info *uarg,
-			   bool success)
+static void msg_zerocopy_complete(struct sk_buff *skb, struct ubuf_info *uarg,
+				  bool success)
 {
 	struct ubuf_info_msgzc *uarg_zc = uarg_to_msgzc(uarg);
 
···
 	if (refcount_dec_and_test(&uarg->refcnt))
 		__msg_zerocopy_callback(uarg_zc);
 }
-EXPORT_SYMBOL_GPL(msg_zerocopy_callback);
 
 void msg_zerocopy_put_abort(struct ubuf_info *uarg, bool have_uref)
 {
···
 	uarg_to_msgzc(uarg)->len--;
 
 	if (have_uref)
-		msg_zerocopy_callback(NULL, uarg, true);
+		msg_zerocopy_complete(NULL, uarg, true);
 }
 EXPORT_SYMBOL_GPL(msg_zerocopy_put_abort);
+
+const struct ubuf_info_ops msg_zerocopy_ubuf_ops = {
+	.complete = msg_zerocopy_complete,
+};
+EXPORT_SYMBOL_GPL(msg_zerocopy_ubuf_ops);
 
 int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb,
 			     struct msghdr *msg, int len,
···
 	struct ubuf_info *orig_uarg = skb_zcopy(skb);
 	int err, orig_len = skb->len;
 
-	/* An skb can only point to one uarg. This edge case happens when
-	 * TCP appends to an skb, but zerocopy_realloc triggered a new alloc.
-	 */
-	if (orig_uarg && uarg != orig_uarg)
-		return -EEXIST;
+	if (uarg->ops->link_skb) {
+		err = uarg->ops->link_skb(skb, uarg);
+		if (err)
+			return err;
+	} else {
+		/* An skb can only point to one uarg. This edge case happens
+		 * when TCP appends to an skb, but zerocopy_realloc triggered
+		 * a new alloc.
+		 */
+		if (orig_uarg && uarg != orig_uarg)
+			return -EEXIST;
+	}
 
 	err = __zerocopy_sg_from_iter(msg, sk, skb, &msg->msg_iter, len);
 	if (err == -EFAULT || (err == -EMSGSIZE && skb->len == orig_len)) {
···
 		return err;
 	}
 
-	skb_zcopy_set(skb, uarg, NULL);
+	if (!uarg->ops->link_skb)
+		skb_zcopy_set(skb, uarg, NULL);
 	return skb->len - orig_len;
 }
 EXPORT_SYMBOL_GPL(skb_zerocopy_iter_stream);