ixgbe: Make better use of memory allocations in one-buffer mode w/ RSC

This patch improves the memory utilization with RSC when in one-buffer
mode.  This is accomplished by making the default buffer sizes match up
with the standard memory allocation sizes minus 1K for shared info and
padding overhead.  By doing this CPU utilization when doing large receives
can be reduced by as much as 8%.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe.h

@@ -72,10 +72,13 @@
 
 /* Supported Rx Buffer Sizes */
 #define IXGBE_RXBUFFER_512   512    /* Used for packet split */
-#define IXGBE_RXBUFFER_2048  2048
-#define IXGBE_RXBUFFER_4096  4096
-#define IXGBE_RXBUFFER_8192  8192
-#define IXGBE_MAX_RXBUFFER   16384  /* largest size for a single descriptor */
+#define IXGBE_RXBUFFER_2K   2048
+#define IXGBE_RXBUFFER_3K   3072
+#define IXGBE_RXBUFFER_4K   4096
+#define IXGBE_RXBUFFER_7K   7168
+#define IXGBE_RXBUFFER_8K   8192
+#define IXGBE_RXBUFFER_15K  15360
+#define IXGBE_MAX_RXBUFFER  16384  /* largest size for a single descriptor */
 
 /*
  * NOTE: netdev_alloc_skb reserves up to 64 bytes, NET_IP_ALIGN mans we

drivers/net/ethernet/intel/ixgbe/ixgbe_ethtool.c

@@ -1539,7 +1539,7 @@ static int ixgbe_setup_desc_rings(struct ixgbe_adapter *adapter)
 	rx_ring->dev = &adapter->pdev->dev;
 	rx_ring->netdev = adapter->netdev;
 	rx_ring->reg_idx = adapter->rx_ring[0]->reg_idx;
-	rx_ring->rx_buf_len = IXGBE_RXBUFFER_2048;
+	rx_ring->rx_buf_len = IXGBE_RXBUFFER_2K;
 	rx_ring->numa_node = adapter->node;
 
 	err = ixgbe_setup_rx_resources(rx_ring);

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -499,7 +499,7 @@ static void ixgbe_dump(struct ixgbe_adapter *adapter)
 					   rx_ring->rx_buf_len, true);
 
 					if (rx_ring->rx_buf_len
-						< IXGBE_RXBUFFER_2048)
+						< IXGBE_RXBUFFER_2K)
 						print_hex_dump(KERN_INFO, "",
 						  DUMP_PREFIX_ADDRESS, 16, 1,
 						  phys_to_virt(
@@ -2644,9 +2644,9 @@ static void ixgbe_configure_rscctl(struct ixgbe_adapter *adapter,
 		rscctrl |= IXGBE_RSCCTL_MAXDESC_1;
 #endif
 	} else {
-		if (rx_buf_len < IXGBE_RXBUFFER_4096)
+		if (rx_buf_len < IXGBE_RXBUFFER_4K)
 			rscctrl |= IXGBE_RSCCTL_MAXDESC_16;
-		else if (rx_buf_len < IXGBE_RXBUFFER_8192)
+		else if (rx_buf_len < IXGBE_RXBUFFER_8K)
 			rscctrl |= IXGBE_RSCCTL_MAXDESC_8;
 		else
 			rscctrl |= IXGBE_RSCCTL_MAXDESC_4;
@@ -2879,17 +2879,6 @@ static void ixgbe_set_rx_buffer_len(struct ixgbe_adapter *adapter)
 	if (hw->mac.type == ixgbe_mac_82599EB)
 		adapter->flags &= ~IXGBE_FLAG_RX_PS_ENABLED;
 
-	/* Set the RX buffer length according to the mode */
-	if (adapter->flags & IXGBE_FLAG_RX_PS_ENABLED) {
-		rx_buf_len = IXGBE_RX_HDR_SIZE;
-	} else {
-		if (!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED) &&
-		    (netdev->mtu <= ETH_DATA_LEN))
-			rx_buf_len = MAXIMUM_ETHERNET_VLAN_SIZE;
-		else
-			rx_buf_len = ALIGN(max_frame + VLAN_HLEN, 1024);
-	}
-
 #ifdef IXGBE_FCOE
 	/* adjust max frame to be able to do baby jumbo for FCoE */
 	if ((adapter->flags & IXGBE_FLAG_FCOE_ENABLED) &&
@@ -2905,6 +2894,30 @@ static void ixgbe_set_rx_buffer_len(struct ixgbe_adapter *adapter)
 		IXGBE_WRITE_REG(hw, IXGBE_MHADD, mhadd);
 	}
 
+	/* MHADD will allow an extra 4 bytes past for vlan tagged frames */
+	max_frame += VLAN_HLEN;
+
+	/* Set the RX buffer length according to the mode */
+	if (adapter->flags & IXGBE_FLAG_RX_PS_ENABLED) {
+		rx_buf_len = IXGBE_RX_HDR_SIZE;
+	} else {
+		if (!(adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED) &&
+		    (netdev->mtu <= ETH_DATA_LEN))
+			rx_buf_len = MAXIMUM_ETHERNET_VLAN_SIZE;
+		/*
+		 * Make best use of allocation by using all but 1K of a
+		 * power of 2 allocation that will be used for skb->head.
+		 */
+		else if (max_frame <= IXGBE_RXBUFFER_3K)
+			rx_buf_len = IXGBE_RXBUFFER_3K;
+		else if (max_frame <= IXGBE_RXBUFFER_7K)
+			rx_buf_len = IXGBE_RXBUFFER_7K;
+		else if (max_frame <= IXGBE_RXBUFFER_15K)
+			rx_buf_len = IXGBE_RXBUFFER_15K;
+		else
+			rx_buf_len = IXGBE_MAX_RXBUFFER;
+	}
+
 	hlreg0 = IXGBE_READ_REG(hw, IXGBE_HLREG0);
 	/* set jumbo enable since MHADD.MFS is keeping size locked at max_frame */
 	hlreg0 |= IXGBE_HLREG0_JUMBOEN;