bmips: convert to build_skb()

We can increase the efficiency of rx path by using buffers to receive
packets then build SKBs around them just before passing into the network
stack. In contrast, preallocating SKBs too early reduces CPU cache
efficiency.
Performance is slightly increased but the changes allow more
potential optimizations.

Signed-off-by: Sieng Piaw Liew <[email protected]>
[improve code format]
Signed-off-by: Álvaro Fernández Rojas <[email protected]>

target/linux/bmips/files/drivers/net/ethernet/broadcom/bcm6368-enetsw.c

@@ -25,6 +25,8 @@
 #define ENETSW_TAG_SIZE			6
 #define ENETSW_MTU_OVERHEAD		(VLAN_ETH_HLEN + VLAN_HLEN + \
 					 ENETSW_TAG_SIZE)
+#define ENETSW_FRAG_SIZE(x)		(SKB_DATA_ALIGN(NET_SKB_PAD + x + \
+					 SKB_DATA_ALIGN(sizeof(struct skb_shared_info))))
 
 /* default number of descriptor */
 #define ENETSW_DEF_RX_DESC		64
@@ -170,13 +172,16 @@ struct bcm6368_enetsw {
 	/* next dirty rx descriptor to refill */
 	int rx_dirty_desc;
 
-	/* size of allocated rx skbs */
-	unsigned int rx_skb_size;
+	/* size of allocated rx buffer */
+	unsigned int rx_buf_size;
 
-	/* list of skb given to hw for rx */
-	struct sk_buff **rx_skb;
+	/* size of allocated rx frag */
+	unsigned int rx_frag_size;
 
-	/* used when rx skb allocation failed, so we defer rx queue
+	/* list of buffer given to hw for rx */
+	unsigned char **rx_buf;
+
+	/* used when rx buffer allocation failed, so we defer rx queue
 	 * refill */
 	struct timer_list rx_timeout;
 
@@ -257,26 +262,27 @@ static int bcm6368_enetsw_refill_rx(struct net_device *dev)
 
 	while (priv->rx_desc_count < priv->rx_ring_size) {
 		struct bcm6368_enetsw_desc *desc;
-		struct sk_buff *skb;
-		dma_addr_t p;
 		int desc_idx;
 		u32 len_stat;
 
 		desc_idx = priv->rx_dirty_desc;
 		desc = &priv->rx_desc_cpu[desc_idx];
 
-		if (!priv->rx_skb[desc_idx]) {
-			skb = netdev_alloc_skb(dev, priv->rx_skb_size);
-			if (!skb)
+		if (!priv->rx_buf[desc_idx]) {
+			unsigned char *buf =
+				netdev_alloc_frag(priv->rx_frag_size);
+
+			if (unlikely(!buf))
 				break;
-			priv->rx_skb[desc_idx] = skb;
-			p = dma_map_single(&priv->pdev->dev, skb->data,
-					   priv->rx_skb_size,
-					   DMA_FROM_DEVICE);
-			desc->address = p;
+
+			priv->rx_buf[desc_idx] = buf;
+			desc->address = dma_map_single(&priv->pdev->dev,
+						       buf + NET_SKB_PAD,
+						       priv->rx_buf_size,
+						       DMA_FROM_DEVICE);
 		}
 
-		len_stat = priv->rx_skb_size << DMADESC_LENGTH_SHIFT;
+		len_stat = priv->rx_buf_size << DMADESC_LENGTH_SHIFT;
 		len_stat |= DMADESC_OWNER_MASK;
 		if (priv->rx_dirty_desc == priv->rx_ring_size - 1) {
 			len_stat |= DMADESC_WRAP_MASK;
@@ -333,7 +339,9 @@ static int bcm6368_enetsw_receive_queue(struct net_device *dev, int budget)
 
 	do {
 		struct bcm6368_enetsw_desc *desc;
+		unsigned int frag_size;
 		struct sk_buff *skb;
+		unsigned char *buf;
 		int desc_idx;
 		u32 len_stat;
 		unsigned int len;
@@ -365,17 +373,17 @@ static int bcm6368_enetsw_receive_queue(struct net_device *dev, int budget)
 		}
 
 		/* valid packet */
-		skb = priv->rx_skb[desc_idx];
+		buf = priv->rx_buf[desc_idx];
 		len = (len_stat & DMADESC_LENGTH_MASK)
 		      >> DMADESC_LENGTH_SHIFT;
 		/* don't include FCS */
 		len -= 4;
 
 		if (len < priv->copybreak) {
-			struct sk_buff *nskb;
+			unsigned int nfrag_size = ENETSW_FRAG_SIZE(len);
+			unsigned char *nbuf = napi_alloc_frag(nfrag_size);
 
-			nskb = netdev_alloc_skb(dev, len);
-			if (!nskb) {
+			if (unlikely(!nbuf)) {
 				/* forget packet, just rearm desc */
 				dev->stats.rx_dropped++;
 				continue;
@@ -383,16 +391,26 @@ static int bcm6368_enetsw_receive_queue(struct net_device *dev, int budget)
 
 			dma_sync_single_for_cpu(kdev, desc->address,
 						len, DMA_FROM_DEVICE);
-			memcpy(nskb->data, skb->data, len);
+			memcpy(nbuf + NET_SKB_PAD, buf + NET_SKB_PAD, len);
 			dma_sync_single_for_device(kdev, desc->address,
 						   len, DMA_FROM_DEVICE);
-			skb = nskb;
+			buf = nbuf;
+			frag_size = nfrag_size;
 		} else {
-			dma_unmap_single(&priv->pdev->dev, desc->address,
-					 priv->rx_skb_size, DMA_FROM_DEVICE);
-			priv->rx_skb[desc_idx] = NULL;
+			dma_unmap_single(kdev, desc->address,
+					 priv->rx_buf_size, DMA_FROM_DEVICE);
+			priv->rx_buf[desc_idx] = NULL;
+			frag_size = priv->rx_frag_size;
+		}
+
+		skb = build_skb(buf, frag_size);
+		if (unlikely(!skb)) {
+			skb_free_frag(buf);
+			dev->stats.rx_dropped++;
+			continue;
 		}
 
+		skb_reserve(skb, NET_SKB_PAD);
 		skb_put(skb, len);
 		skb->protocol = eth_type_trans(skb, dev);
 		dev->stats.rx_packets++;
@@ -680,7 +698,7 @@ static int bcm6368_enetsw_open(struct net_device *dev)
 	priv->tx_skb = kzalloc(sizeof(struct sk_buff *) * priv->tx_ring_size,
 			       GFP_KERNEL);
 	if (!priv->tx_skb) {
-		dev_err(kdev, "cannot allocate rx skb queue\n");
+		dev_err(kdev, "cannot allocate tx skb queue\n");
 		ret = -ENOMEM;
 		goto out_free_tx_ring;
 	}
@@ -690,11 +708,11 @@ static int bcm6368_enetsw_open(struct net_device *dev)
 	priv->tx_curr_desc = 0;
 	spin_lock_init(&priv->tx_lock);
 
-	/* init & fill rx ring with skbs */
-	priv->rx_skb = kzalloc(sizeof(struct sk_buff *) * priv->rx_ring_size,
+	/* init & fill rx ring with buffers */
+	priv->rx_buf = kzalloc(sizeof(unsigned char *) * priv->rx_ring_size,
 			       GFP_KERNEL);
-	if (!priv->rx_skb) {
-		dev_err(kdev, "cannot allocate rx skb queue\n");
+	if (!priv->rx_buf) {
+		dev_err(kdev, "cannot allocate rx buffer queue\n");
 		ret = -ENOMEM;
 		goto out_free_tx_skb;
 	}
@@ -708,7 +726,7 @@ static int bcm6368_enetsw_open(struct net_device *dev)
 		   DMA_BUFALLOC_REG(priv->rx_chan));
 
 	if (bcm6368_enetsw_refill_rx(dev)) {
-		dev_err(kdev, "cannot allocate rx skb queue\n");
+		dev_err(kdev, "cannot allocate rx buffer queue\n");
 		ret = -ENOMEM;
 		goto out;
 	}
@@ -770,15 +788,15 @@ out:
 	for (i = 0; i < priv->rx_ring_size; i++) {
 		struct bcm6368_enetsw_desc *desc;
 
-		if (!priv->rx_skb[i])
+		if (!priv->rx_buf[i])
 			continue;
 
 		desc = &priv->rx_desc_cpu[i];
-		dma_unmap_single(kdev, desc->address, priv->rx_skb_size,
+		dma_unmap_single(kdev, desc->address, priv->rx_buf_size,
 				 DMA_FROM_DEVICE);
-		kfree_skb(priv->rx_skb[i]);
+		skb_free_frag(priv->rx_buf[i]);
 	}
-	kfree(priv->rx_skb);
+	kfree(priv->rx_buf);
 
 out_free_tx_skb:
 	kfree(priv->tx_skb);
@@ -823,22 +841,22 @@ static int bcm6368_enetsw_stop(struct net_device *dev)
 	/* force reclaim of all tx buffers */
 	bcm6368_enetsw_tx_reclaim(dev, 1);
 
-	/* free the rx skb ring */
+	/* free the rx buffer ring */
 	for (i = 0; i < priv->rx_ring_size; i++) {
 		struct bcm6368_enetsw_desc *desc;
 
-		if (!priv->rx_skb[i])
+		if (!priv->rx_buf[i])
 			continue;
 
 		desc = &priv->rx_desc_cpu[i];
-		dma_unmap_single_attrs(kdev, desc->address, priv->rx_skb_size,
+		dma_unmap_single_attrs(kdev, desc->address, priv->rx_buf_size,
 				       DMA_FROM_DEVICE,
 				       DMA_ATTR_SKIP_CPU_SYNC);
-		kfree_skb(priv->rx_skb[i]);
+		skb_free_frag(priv->rx_buf[i]);
 	}
 
 	/* free remaining allocated memory */
-	kfree(priv->rx_skb);
+	kfree(priv->rx_buf);
 	kfree(priv->tx_skb);
 	dma_free_coherent(kdev, priv->rx_desc_alloc_size,
 			  priv->rx_desc_cpu, priv->rx_desc_dma);
@@ -960,9 +978,11 @@ static int bcm6368_enetsw_probe(struct platform_device *pdev)
 		dev_info(dev, "random mac %pM\n", ndev->dev_addr);
 	}
 
-	priv->rx_skb_size = ALIGN(ndev->mtu + ENETSW_MTU_OVERHEAD,
+	priv->rx_buf_size = ALIGN(ndev->mtu + ENETSW_MTU_OVERHEAD,
 				  priv->dma_maxburst * 4);
 
+	priv->rx_frag_size = ENETSW_FRAG_SIZE(priv->rx_buf_size);
+
 	priv->num_clocks = of_clk_get_parent_count(node);
 	if (priv->num_clocks) {
 		priv->clock = devm_kcalloc(dev, priv->num_clocks,