[RFC net-next v1 07/12] virtio_net: refactor the xmit type

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Because the af-xdp will introduce a new xmit type, so I refactor the
xmit type mechanism first.

In general, pointers are aligned to 4 or 8 bytes. If it is aligned to 4
bytes, then only two bits are free for a pointer. But there are 4 types
here, so we can't use bits to distinguish them. And 2 bits is enough for
4 types:

    00 for skb
    01 for SKB_ORPHAN
    10 for XDP
    11 for af-xdp tx

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
 drivers/net/virtio_net.c | 90 +++++++++++++++++++++++-----------------
 1 file changed, 51 insertions(+), 39 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 630e5b21ad69..41a5ea9b788d 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -45,9 +45,6 @@ module_param(napi_tx, bool, 0644);
 #define VIRTIO_XDP_TX		BIT(0)
 #define VIRTIO_XDP_REDIR	BIT(1)
 
-#define VIRTIO_XDP_FLAG		BIT(0)
-#define VIRTIO_ORPHAN_FLAG	BIT(1)
-
 /* RX packet size EWMA. The average packet size is used to determine the packet
  * buffer size when refilling RX rings. As the entire RX ring may be refilled
  * at once, the weight is chosen so that the EWMA will be insensitive to short-
@@ -512,34 +509,35 @@ static struct sk_buff *virtnet_skb_append_frag(struct sk_buff *head_skb,
 					       struct page *page, void *buf,
 					       int len, int truesize);
 
-static bool is_xdp_frame(void *ptr)
-{
-	return (unsigned long)ptr & VIRTIO_XDP_FLAG;
-}
+enum virtnet_xmit_type {
+	VIRTNET_XMIT_TYPE_SKB,
+	VIRTNET_XMIT_TYPE_SKB_ORPHAN,
+	VIRTNET_XMIT_TYPE_XDP,
+};
 
-static void *xdp_to_ptr(struct xdp_frame *ptr)
-{
-	return (void *)((unsigned long)ptr | VIRTIO_XDP_FLAG);
-}
+/* We use the last two bits of the pointer to distinguish the xmit type. */
+#define VIRTNET_XMIT_TYPE_MASK (BIT(0) | BIT(1))
 
-static struct xdp_frame *ptr_to_xdp(void *ptr)
+static enum virtnet_xmit_type virtnet_xmit_ptr_strip(void **ptr)
 {
-	return (struct xdp_frame *)((unsigned long)ptr & ~VIRTIO_XDP_FLAG);
-}
+	unsigned long p = (unsigned long)*ptr;
 
-static bool is_orphan_skb(void *ptr)
-{
-	return (unsigned long)ptr & VIRTIO_ORPHAN_FLAG;
+	*ptr = (void *)(p & ~VIRTNET_XMIT_TYPE_MASK);
+
+	return p & VIRTNET_XMIT_TYPE_MASK;
 }
 
-static void *skb_to_ptr(struct sk_buff *skb, bool orphan)
+static void *virtnet_xmit_ptr_mix(void *ptr, enum virtnet_xmit_type type)
 {
-	return (void *)((unsigned long)skb | (orphan ? VIRTIO_ORPHAN_FLAG : 0));
+	return (void *)((unsigned long)ptr | type);
 }
 
-static struct sk_buff *ptr_to_skb(void *ptr)
+static int virtnet_add_outbuf(struct send_queue *sq, int num, void *data,
+			      enum virtnet_xmit_type type)
 {
-	return (struct sk_buff *)((unsigned long)ptr & ~VIRTIO_ORPHAN_FLAG);
+	return virtqueue_add_outbuf(sq->vq, sq->sg, num,
+				    virtnet_xmit_ptr_mix(data, type),
+				    GFP_ATOMIC);
 }
 
 static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
@@ -552,29 +550,37 @@ static void sg_fill_dma(struct scatterlist *sg, dma_addr_t addr, u32 len)
 static void __free_old_xmit(struct send_queue *sq, struct netdev_queue *txq,
 			    bool in_napi, struct virtnet_sq_free_stats *stats)
 {
+	struct xdp_frame *frame;
+	struct sk_buff *skb;
 	unsigned int len;
 	void *ptr;
 
 	while ((ptr = virtqueue_get_buf(sq->vq, &len)) != NULL) {
-		if (!is_xdp_frame(ptr)) {
-			struct sk_buff *skb = ptr_to_skb(ptr);
+		switch (virtnet_xmit_ptr_strip(&ptr)) {
+		case VIRTNET_XMIT_TYPE_SKB:
+			skb = ptr;
 
 			pr_debug("Sent skb %p\n", skb);
+			stats->napi_packets++;
+			stats->napi_bytes += skb->len;
+			napi_consume_skb(skb, in_napi);
+			break;
 
-			if (is_orphan_skb(ptr)) {
-				stats->packets++;
-				stats->bytes += skb->len;
-			} else {
-				stats->napi_packets++;
-				stats->napi_bytes += skb->len;
-			}
+		case VIRTNET_XMIT_TYPE_SKB_ORPHAN:
+			skb = ptr;
+
+			stats->packets++;
+			stats->bytes += skb->len;
 			napi_consume_skb(skb, in_napi);
-		} else {
-			struct xdp_frame *frame = ptr_to_xdp(ptr);
+			break;
+
+		case VIRTNET_XMIT_TYPE_XDP:
+			frame = ptr;
 
 			stats->packets++;
 			stats->bytes += xdp_get_frame_len(frame);
 			xdp_return_frame(frame);
+			break;
 		}
 	}
 	netdev_tx_completed_queue(txq, stats->napi_packets, stats->napi_bytes);
@@ -1431,8 +1437,7 @@ static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
 			    skb_frag_size(frag), skb_frag_off(frag));
 	}
 
-	err = virtqueue_add_outbuf(sq->vq, sq->sg, nr_frags + 1,
-				   xdp_to_ptr(xdpf), GFP_ATOMIC);
+	err = virtnet_add_outbuf(sq, nr_frags + 1, xdpf, VIRTNET_XMIT_TYPE_XDP);
 	if (unlikely(err))
 		return -ENOSPC; /* Caller handle free/refcnt */
 
@@ -3040,8 +3045,9 @@ static int xmit_skb(struct send_queue *sq, struct sk_buff *skb, bool orphan)
 			return num_sg;
 		num_sg++;
 	}
-	return virtqueue_add_outbuf(sq->vq, sq->sg, num_sg,
-				    skb_to_ptr(skb, orphan), GFP_ATOMIC);
+
+	return virtnet_add_outbuf(sq, num_sg, skb,
+				  orphan ? VIRTNET_XMIT_TYPE_SKB_ORPHAN : VIRTNET_XMIT_TYPE_SKB);
 }
 
 static netdev_tx_t start_xmit(struct sk_buff *skb, struct net_device *dev)
@@ -5918,10 +5924,16 @@ static void free_receive_page_frags(struct virtnet_info *vi)
 
 static void virtnet_sq_free_unused_buf(struct virtqueue *vq, void *buf)
 {
-	if (!is_xdp_frame(buf))
+	switch (virtnet_xmit_ptr_strip(&buf)) {
+	case VIRTNET_XMIT_TYPE_SKB:
+	case VIRTNET_XMIT_TYPE_SKB_ORPHAN:
 		dev_kfree_skb(buf);
-	else
-		xdp_return_frame(ptr_to_xdp(buf));
+		break;
+
+	case VIRTNET_XMIT_TYPE_XDP:
+		xdp_return_frame(buf);
+		break;
+	}
 }
 
 static void free_unused_bufs(struct virtnet_info *vi)
-- 
2.32.0.3.g01195cf9f





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