Re: [PATCH net-next 1/2] vsock/virtio: refactor virtio_transport_send_pkt_work

From: Marco Pinna <redacted>

This is a preliminary patch to introduce an optimization to
the enqueue system.

All the code used to enqueue a packet into the virtqueue
is removed from virtio_transport_send_pkt_work()
and moved to the new virtio_transport_send_skb() function.

Co-developed-by: Luigi Leonardi <redacted>
Signed-off-by: Luigi Leonardi <redacted>
Signed-off-by: Marco Pinna <redacted>
---
net/vmw_vsock/virtio_transport.c | 134 +++++++++++++++++--------------
1 file changed, 74 insertions(+), 60 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport.c b/net/vmw_vsock/virtio_transport.c
index 43d405298857..c930235ecaec 100644
--- a/net/vmw_vsock/virtio_transport.c
+++ b/net/vmw_vsock/virtio_transport.c

@@ -94,6 +94,78 @@ static u32 virtio_transport_get_local_cid(void)

	return ret;
}

+/* Caller need to hold vsock->tx_lock on vq */
+static int virtio_transport_send_skb(struct sk_buff *skb, struct virtqueue *vq,
+				     struct virtio_vsock *vsock, bool *restart_rx)
+{
+	int ret, in_sg = 0, out_sg = 0;
+	struct scatterlist **sgs;
+	bool reply;
+
+	reply = virtio_vsock_skb_reply(skb);
+	sgs = vsock->out_sgs;
+	sg_init_one(sgs[out_sg], virtio_vsock_hdr(skb),
+		    sizeof(*virtio_vsock_hdr(skb)));
+	out_sg++;
+
+	if (!skb_is_nonlinear(skb)) {
+		if (skb->len > 0) {
+			sg_init_one(sgs[out_sg], skb->data, skb->len);
+			out_sg++;
+		}
+	} else {
+		struct skb_shared_info *si;
+		int i;
+
+		/* If skb is nonlinear, then its buffer must contain
+		 * only header and nothing more. Data is stored in
+		 * the fragged part.
+		 */
+		WARN_ON_ONCE(skb_headroom(skb) != sizeof(*virtio_vsock_hdr(skb)));
+
+		si = skb_shinfo(skb);
+
+		for (i = 0; i < si->nr_frags; i++) {
+			skb_frag_t *skb_frag = &si->frags[i];
+			void *va;
+
+			/* We will use 'page_to_virt()' for the userspace page
+			 * here, because virtio or dma-mapping layers will call
+			 * 'virt_to_phys()' later to fill the buffer descriptor.
+			 * We don't touch memory at "virtual" address of 
this page.
+			 */
+			va = page_to_virt(skb_frag_page(skb_frag));
+			sg_init_one(sgs[out_sg],
+				    va + skb_frag_off(skb_frag),
+				    skb_frag_size(skb_frag));
+			out_sg++;
+		}
+	}
+
+	ret = virtqueue_add_sgs(vq, sgs, out_sg, in_sg, skb, GFP_KERNEL);
+	/* Usually this means that there is no more space available in
+	 * the vq
+	 */
+	if (ret < 0)
+		goto out;

+out:
+	return ret;
+}
+
static void
virtio_transport_send_pkt_work(struct work_struct *work)
{

@@ -111,77 +183,19 @@ virtio_transport_send_pkt_work(struct work_struct *work)

	vq = vsock->vqs[VSOCK_VQ_TX];

	for (;;) {
-		int ret, in_sg = 0, out_sg = 0;
-		struct scatterlist **sgs;
		struct sk_buff *skb;
-		bool reply;
+		int ret;

		skb = virtio_vsock_skb_dequeue(&vsock->send_pkt_queue);
		if (!skb)
			break;

-		reply = virtio_vsock_skb_reply(skb);
-		sgs = vsock->out_sgs;
-		sg_init_one(sgs[out_sg], virtio_vsock_hdr(skb),
-			    sizeof(*virtio_vsock_hdr(skb)));
-		out_sg++;
-
-		if (!skb_is_nonlinear(skb)) {
-			if (skb->len > 0) {
-				sg_init_one(sgs[out_sg], skb->data, skb->len);
-				out_sg++;
-			}
-		} else {
-			struct skb_shared_info *si;
-			int i;
+		ret = virtio_transport_send_skb(skb, vq, vsock, &restart_rx);