linux-kernel - [RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

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Date:   Sun, 19 Mar 2023 21:46:10 +0300
From:   Arseniy Krasnov <avkrasnov@...rdevices.ru>
To:     Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>
CC:     <kvm@...r.kernel.org>, <virtualization@...ts.linux-foundation.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...rdevices.ru>, <oxffffaa@...il.com>,
        <avkrasnov@...rdevices.ru>
Subject: [RFC PATCH v2] virtio/vsock: allocate multiple skbuffs on tx

This adds small optimization for tx path: instead of allocating single
skbuff on every call to transport, allocate multiple skbuff's until
credit space allows, thus trying to send as much as possible data without
return to af_vsock.c.

Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
---
 Link to v1:
 https://lore.kernel.org/netdev/2c52aa26-8181-d37a-bccd-a86bd3cbc6e1@sberdevices.ru/

 Changelog:
 v1 -> v2:
 - If sent something, return number of bytes sent (even in
   case of error). Return error only if failed to sent first
   skbuff.

 net/vmw_vsock/virtio_transport_common.c | 53 ++++++++++++++++++-------
 1 file changed, 39 insertions(+), 14 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index 6564192e7f20..3fdf1433ec28 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -196,7 +196,8 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	const struct virtio_transport *t_ops;
 	struct virtio_vsock_sock *vvs;
 	u32 pkt_len = info->pkt_len;
-	struct sk_buff *skb;
+	u32 rest_len;
+	int ret;
 
 	info->type = virtio_transport_get_type(sk_vsock(vsk));
 
@@ -216,10 +217,6 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 
 	vvs = vsk->trans;
 
-	/* we can send less than pkt_len bytes */
-	if (pkt_len > VIRTIO_VSOCK_MAX_PKT_BUF_SIZE)
-		pkt_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE;
-
 	/* virtio_transport_get_credit might return less than pkt_len credit */
 	pkt_len = virtio_transport_get_credit(vvs, pkt_len);
 
@@ -227,17 +224,45 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk,
 	if (pkt_len == 0 && info->op == VIRTIO_VSOCK_OP_RW)
 		return pkt_len;
 
-	skb = virtio_transport_alloc_skb(info, pkt_len,
-					 src_cid, src_port,
-					 dst_cid, dst_port);
-	if (!skb) {
-		virtio_transport_put_credit(vvs, pkt_len);
-		return -ENOMEM;
-	}
+	ret = 0;
+	rest_len = pkt_len;
+
+	do {
+		struct sk_buff *skb;
+		size_t skb_len;
+
+		skb_len = min_t(u32, VIRTIO_VSOCK_MAX_PKT_BUF_SIZE, rest_len);
+
+		skb = virtio_transport_alloc_skb(info, skb_len,
+						 src_cid, src_port,
+						 dst_cid, dst_port);
+		if (!skb) {
+			ret = -ENOMEM;
+			break;
+		}
+
+		virtio_transport_inc_tx_pkt(vvs, skb);
+
+		ret = t_ops->send_pkt(skb);
+
+		if (ret < 0)
+			break;
 
-	virtio_transport_inc_tx_pkt(vvs, skb);
+		rest_len -= skb_len;
+	} while (rest_len);
 
-	return t_ops->send_pkt(skb);
+	/* Don't call this function with zero as argument:
+	 * it tries to acquire spinlock and such argument
+	 * makes this call useless.
+	 */
+	if (rest_len)
+		virtio_transport_put_credit(vvs, rest_len);
+
+	/* Return number of bytes, if any data has been sent. */
+	if (rest_len != pkt_len)
+		ret = pkt_len - rest_len;
+
+	return ret;
 }
 
 static bool virtio_transport_inc_rx_pkt(struct virtio_vsock_sock *vvs,
-- 
2.25.1