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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@sberdevices.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
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