igb: Change Tx cleanup loop to do/while instead of for

This change makes it so that Tx cleanup is done in a do/while loop instead
of a for loop.  The main motivation behind this is the fact that we should
never be invoked with a budget less than 1 so we can skip checking the
budget before processing the first descriptor.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index c9997d8..91f542c 100644 (file)
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -5690,7 +5690,7 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
        struct igb_adapter *adapter = q_vector->adapter;
        struct igb_ring *tx_ring = q_vector->tx.ring;
        struct igb_tx_buffer *tx_buffer;
-       union e1000_adv_tx_desc *tx_desc, *eop_desc;
+       union e1000_adv_tx_desc *tx_desc;
        unsigned int total_bytes = 0, total_packets = 0;
        unsigned int budget = q_vector->tx.work_limit;
        unsigned int i = tx_ring->next_to_clean;
@@ -5702,16 +5702,16 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
        tx_desc = IGB_TX_DESC(tx_ring, i);
        i -= tx_ring->count;
 
-       for (; budget; budget--) {
-               eop_desc = tx_buffer->next_to_watch;
-
-               /* prevent any other reads prior to eop_desc */
-               rmb();
+       do {
+               union e1000_adv_tx_desc *eop_desc = tx_buffer->next_to_watch;
 
                /* if next_to_watch is not set then there is no work pending */
                if (!eop_desc)
                        break;
 
+               /* prevent any other reads prior to eop_desc */
+               rmb();
+
                /* if DD is not set pending work has not been completed */
                if (!(eop_desc->wb.status & cpu_to_le32(E1000_TXD_STAT_DD)))
                        break;
@@ -5767,7 +5767,13 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
                        tx_buffer = tx_ring->tx_buffer_info;
                        tx_desc = IGB_TX_DESC(tx_ring, 0);
                }
-       }
+
+               /* issue prefetch for next Tx descriptor */
+               prefetch(tx_desc);
+
+               /* update budget accounting */
+               budget--;
+       } while (likely(budget));
 
        netdev_tx_completed_queue(txring_txq(tx_ring),
                                  total_packets, total_bytes);
@@ -5783,12 +5789,10 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
        if (test_bit(IGB_RING_FLAG_TX_DETECT_HANG, &tx_ring->flags)) {
                struct e1000_hw *hw = &adapter->hw;
 
-               eop_desc = tx_buffer->next_to_watch;
-
                /* Detect a transmit hang in hardware, this serializes the
                 * check with the clearing of time_stamp and movement of i */
                clear_bit(IGB_RING_FLAG_TX_DETECT_HANG, &tx_ring->flags);
-               if (eop_desc &&
+               if (tx_buffer->next_to_watch &&
                    time_after(jiffies, tx_buffer->time_stamp +
                               (adapter->tx_timeout_factor * HZ)) &&
                    !(rd32(E1000_STATUS) & E1000_STATUS_TXOFF)) {
@@ -5812,9 +5816,9 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
                                tx_ring->next_to_use,
                                tx_ring->next_to_clean,
                                tx_buffer->time_stamp,
-                               eop_desc,
+                               tx_buffer->next_to_watch,
                                jiffies,
-                               eop_desc->wb.status);
+                               tx_buffer->next_to_watch->wb.status);
                        netif_stop_subqueue(tx_ring->netdev,
                                            tx_ring->queue_index);