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>

1 files changed, 18 insertions, 11 deletions

diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
index b53f26501173..4ab17ab7fbce 100644
--- a/drivers/net/ixgbe/ixgbe_main.c
+++ b/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 */