netdev - [RFC][PATCH 2/2] bgmac: pass received packet to the netif instead of copying it

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Message-Id: <1376243355-5740-2-git-send-email-zajec5@gmail.com>
Date:	Sun, 11 Aug 2013 19:49:15 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	netdev@...r.kernel.org, openwrt-devel@...ts.openwrt.org,
	Hauke Mehrtens <hauke@...ke-m.de>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jonas Gorski <jogo@...nwrt.org>,
	Robert Bradley <robert.bradley1@...il.com>
Cc:	Rafał Miłecki <zajec5@...il.com>
Subject: [RFC][PATCH 2/2] bgmac: pass received packet to the netif instead of copying it

It makes more sense to allocate new (empty) skb and pass it to the
hardware. That way we avoid copying whole packet into new skb which
should result in better performance.
---
 drivers/net/ethernet/broadcom/bgmac.c |   74 ++++++++++++++++++++++++---------
 1 file changed, 54 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bgmac.c b/drivers/net/ethernet/broadcom/bgmac.c
index e70ee43..425fe81 100644
--- a/drivers/net/ethernet/broadcom/bgmac.c
+++ b/drivers/net/ethernet/broadcom/bgmac.c
@@ -304,9 +304,9 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
 		struct device *dma_dev = bgmac->core->dma_dev;
 		struct bgmac_slot_info *slot = &ring->slots[ring->start];
 		struct sk_buff *skb = slot->skb;
-		struct sk_buff *new_skb;
 		struct bgmac_rx_header *rx;
 		u16 len, flags;
+		bool resync_skb = true;
 
 		/* Unmap buffer to make it accessible to the CPU */
 		dma_sync_single_for_cpu(dma_dev, slot->dma_addr,
@@ -317,36 +317,70 @@ static int bgmac_dma_rx_read(struct bgmac *bgmac, struct bgmac_dma_ring *ring,
 		len = le16_to_cpu(rx->len);
 		flags = le16_to_cpu(rx->flags);
 
-		/* Check for poison and drop or pass the packet */
-		if (len == 0xdead && flags == 0xbeef) {
-			bgmac_err(bgmac, "Found poisoned packet at slot %d, DMA issue!\n",
-				  ring->start);
-		} else {
+		do {
+			/* Check for poisoned packet */
+			if (len == 0xdead && flags == 0xbeef) {
+				bgmac_err(bgmac, "Found poisoned packet at slot %d, DMA issue!\n",
+					  ring->start);
+				break;
+			}
+
 			/* Omit CRC. */
 			len -= ETH_FCS_LEN;
 
-			new_skb = netdev_alloc_skb_ip_align(bgmac->net_dev, len);
-			if (new_skb) {
+			/* Use skb_copy for small packets only */
+			if (len > 1) {
+				dma_addr_t old_dma_addr = slot->dma_addr;
+				int err;
+
+				/* Prepare new skb for further packets */
+				err = bgmac_dma_rx_skb_for_slot(bgmac, slot);
+				if (err) {
+					bgmac_err(bgmac, "Couldn't allocate new skb for slot %d!\n",
+						  ring->start);
+					bgmac->net_dev->stats.rx_dropped++;
+					break;
+				}
+				bgmac_dma_rx_setup_desc(bgmac, ring,
+							ring->start);
+
+				/* Unmap old skb, we'll pass it to the netfif */
+				dma_unmap_single(dma_dev, old_dma_addr,
+						 BGMAC_RX_BUF_SIZE,
+						 DMA_FROM_DEVICE);
+				resync_skb = false;
+
+				skb_put(skb, BGMAC_RX_FRAME_OFFSET + len);
+				skb_pull(skb, BGMAC_RX_FRAME_OFFSET);
+			} else {
+				struct sk_buff *new_skb;
+
+				/* Poison the old skb */
+				rx->len = cpu_to_le16(0xdead);
+				rx->flags = cpu_to_le16(0xbeef);
+
+				new_skb = netdev_alloc_skb_ip_align(bgmac->net_dev, len);
+				if (!new_skb) {
+					bgmac_err(bgmac, "Allocation of skb for copying packet failed!\n");
+					bgmac->net_dev->stats.rx_dropped++;
+					break;
+				}
+
 				skb_put(new_skb, len);
 				skb_copy_from_linear_data_offset(skb, BGMAC_RX_FRAME_OFFSET,
 								 new_skb->data,
 								 len);
-				skb_checksum_none_assert(skb);
-				new_skb->protocol =
-					eth_type_trans(new_skb, bgmac->net_dev);
-				netif_receive_skb(new_skb);
-				handled++;
-			} else {
-				bgmac->net_dev->stats.rx_dropped++;
-				bgmac_err(bgmac, "Allocation of skb for copying packet failed!\n");
+				skb = new_skb;
 			}
 
-			/* Poison the old skb */
-			rx->len = cpu_to_le16(0xdead);
-			rx->flags = cpu_to_le16(0xbeef);
-		}
+			skb_checksum_none_assert(skb);
+			skb->protocol = eth_type_trans(skb, bgmac->net_dev);
+			netif_receive_skb(skb);
+			handled++;
+		} while (0);
 
 		/* Make it back accessible to the hardware */
+		if (resync_skb)
 		dma_sync_single_for_device(dma_dev, slot->dma_addr,
 					   BGMAC_RX_BUF_SIZE, DMA_FROM_DEVICE);
 
-- 
1.7.10.4

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