ixgbe: set max desc to prevent total RSC packet size of 64K

The performance of hardware RSC is greatly reduced if the total for max rsc
descriptors multiplied by the buffer size is greater than 65535.  To
prevent this we need to adjust the max rsc descriptors appropriately.
Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ixgbe/ixgbe.h

@@ -75,6 +75,8 @@
 #define IXGBE_RXBUFFER_128   128    /* Used for packet split */
 #define IXGBE_RXBUFFER_256   256    /* 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_RX_HDR_SIZE IXGBE_RXBUFFER_256

drivers/net/ixgbe/ixgbe_main.c

@@ -1995,21 +1995,28 @@ static void ixgbe_configure_rx(struct ixgbe_adapter *adapter)
 			rscctrl = IXGBE_READ_REG(hw, IXGBE_RSCCTL(j));
 			rscctrl |= IXGBE_RSCCTL_RSCEN;
 			/*
-			 *  if packet split is enabled we can only support up
-			 *  to max frags + 1 descriptors.
+			 * we must limit the number of descriptors so that the
+			 * total size of max desc * buf_len is not greater
+			 * than 65535
 			 */
-			if (adapter->flags & IXGBE_FLAG_RX_PS_ENABLED)
-#if (MAX_SKB_FRAGS < 3)
-				rscctrl |= IXGBE_RSCCTL_MAXDESC_1;
-#elif (MAX_SKB_FRAGS < 7)
-				rscctrl |= IXGBE_RSCCTL_MAXDESC_4;
-#elif (MAX_SKB_FRAGS < 15)
+			if (adapter->flags & IXGBE_FLAG_RX_PS_ENABLED) {
+#if (MAX_SKB_FRAGS > 16)
+				rscctrl |= IXGBE_RSCCTL_MAXDESC_16;
+#elif (MAX_SKB_FRAGS > 8)
 				rscctrl |= IXGBE_RSCCTL_MAXDESC_8;
+#elif (MAX_SKB_FRAGS > 4)
+				rscctrl |= IXGBE_RSCCTL_MAXDESC_4;
 #else
-				rscctrl |= IXGBE_RSCCTL_MAXDESC_16;
+				rscctrl |= IXGBE_RSCCTL_MAXDESC_1;
 #endif
-			else
-				rscctrl |= IXGBE_RSCCTL_MAXDESC_16;
+			} else {
+				if (rx_buf_len < IXGBE_RXBUFFER_4096)
+					rscctrl |= IXGBE_RSCCTL_MAXDESC_16;
+				else if (rx_buf_len < IXGBE_RXBUFFER_8192)
+					rscctrl |= IXGBE_RSCCTL_MAXDESC_8;
+				else
+					rscctrl |= IXGBE_RSCCTL_MAXDESC_4;
+			}
 			IXGBE_WRITE_REG(hw, IXGBE_RSCCTL(j), rscctrl);
 		}
 		/* Disable RSC for ACK packets */