e1000e: reduce writes of RX producer ptr

Reduce number of writes to RX producer pointer.   When alloc'ing RX
buffers, only write the RX producer pointer once every
E1000_RX_BUFFER_WRITE (16) buffers created.

Signed-off-by: Tom Herbert <therbert@google.com>
Acked-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 23 insertions, 34 deletions

diff --git a/drivers/net/e1000e/netdev.c b/drivers/net/e1000e/netdev.c
index 8de64ed8762c..b049d1a3c861 100644
--- a/drivers/net/e1000e/netdev.c
+++ b/drivers/net/e1000e/netdev.c
@@ -548,26 +548,23 @@ map_skb:
                 rx_desc = E1000_RX_DESC(*rx_ring, i);
                 rx_desc->buffer_addr = cpu_to_le64(buffer_info->dma);
 
+                if (unlikely(!(i & (E1000_RX_BUFFER_WRITE - 1)))) {
+                        /*
+                         * Force memory writes to complete before letting h/w
+                         * know there are new descriptors to fetch.  (Only
+                         * applicable for weak-ordered memory model archs,
+                         * such as IA-64).
+                         */
+                        wmb();
+                        writel(i, adapter->hw.hw_addr + rx_ring->tail);
+                }
                 i++;
                 if (i == rx_ring->count)
                         i = 0;
                 buffer_info = &rx_ring->buffer_info[i];
         }
 
-        if (rx_ring->next_to_use != i) {
-                rx_ring->next_to_use = i;
-                if (i-- == 0)
-                        i = (rx_ring->count - 1);
-
-                /*
-                 * Force memory writes to complete before letting h/w
-                 * know there are new descriptors to fetch.  (Only
-                 * applicable for weak-ordered memory model archs,
-                 * such as IA-64).
-                 */
-                wmb();
-                writel(i, adapter->hw.hw_addr + rx_ring->tail);
-        }
+        rx_ring->next_to_use = i;
 }
 
 /**
@@ -649,6 +646,17 @@ static void e1000_alloc_rx_buffers_ps(struct e1000_adapter *adapter,
 
                 rx_desc->read.buffer_addr[0] = cpu_to_le64(buffer_info->dma);
 
+                if (unlikely(!(i & (E1000_RX_BUFFER_WRITE - 1)))) {
+                        /*
+                         * Force memory writes to complete before letting h/w
+                         * know there are new descriptors to fetch.  (Only
+                         * applicable for weak-ordered memory model archs,
+                         * such as IA-64).
+                         */
+                        wmb();
+                        writel(i<<1, adapter->hw.hw_addr + rx_ring->tail);
+                }
+
                 i++;
                 if (i == rx_ring->count)
                         i = 0;
@@ -656,26 +664,7 @@ static void e1000_alloc_rx_buffers_ps(struct e1000_adapter *adapter,
         }
 
 no_buffers:
-        if (rx_ring->next_to_use != i) {
-                rx_ring->next_to_use = i;
-
-                if (!(i--))
-                        i = (rx_ring->count - 1);
-
-                /*
-                 * Force memory writes to complete before letting h/w
-                 * know there are new descriptors to fetch.  (Only
-                 * applicable for weak-ordered memory model archs,
-                 * such as IA-64).
-                 */
-                wmb();
-                /*
-                 * Hardware increments by 16 bytes, but packet split
-                 * descriptors are 32 bytes...so we increment tail
-                 * twice as much.
-                 */
-                writel(i<<1, adapter->hw.hw_addr + rx_ring->tail);
-        }
+        rx_ring->next_to_use = i;
 }
 
 /**