igb: Make first and tx_buffer_info->next_to_watch into pointers

This change converts two tx_buffer_info index values into pointers.  The
advantage to this is that we reduce unnecessary computations and in the case
of next_to_watch we get an added bonus of the value being able to provide
additional information as a NULL value indicates it is unset versus a 0 not
having any meaning for the index value.

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>

2 files changed, 37 insertions, 31 deletions

diff --git a/drivers/net/ethernet/intel/igb/igb.h b/drivers/net/ethernet/intel/igb/igb.h
index 56c68fc8bca..7185667bf26 100644
--- a/drivers/net/ethernet/intel/igb/igb.h
+++ b/drivers/net/ethernet/intel/igb/igb.h
@@ -133,7 +133,7 @@ struct vf_data_storage {
 /* wrapper around a pointer to a socket buffer,
  * so a DMA handle can be stored along with the buffer */
 struct igb_tx_buffer {
-        u16 next_to_watch;
+        union e1000_adv_tx_desc *next_to_watch;
         unsigned long time_stamp;
         dma_addr_t dma;
         u32 length;
diff --git a/drivers/net/ethernet/intel/igb/igb_main.c b/drivers/net/ethernet/intel/igb/igb_main.c
index a0bb81d9ef1..edc2caeb6c1 100644
--- a/drivers/net/ethernet/intel/igb/igb_main.c
+++ b/drivers/net/ethernet/intel/igb/igb_main.c
@@ -381,7 +381,7 @@ static void igb_dump(struct igb_adapter *adapter)
                 struct igb_tx_buffer *buffer_info;
                 tx_ring = adapter->tx_ring[n];
                 buffer_info = &tx_ring->tx_buffer_info[tx_ring->next_to_clean];
-                printk(KERN_INFO " %5d %5X %5X %016llX %04X %3X %016llX\n",
+                printk(KERN_INFO " %5d %5X %5X %016llX %04X %p %016llX\n",
                            n, tx_ring->next_to_use, tx_ring->next_to_clean,
                            (u64)buffer_info->dma,
                            buffer_info->length,
@@ -421,7 +421,7 @@ static void igb_dump(struct igb_adapter *adapter)
                         buffer_info = &tx_ring->tx_buffer_info[i];
                         u0 = (struct my_u0 *)tx_desc;
                         printk(KERN_INFO "T [0x%03X]    %016llX %016llX %016llX"
-                                " %04X  %3X %016llX %p", i,
+                                " %04X  %p %016llX %p", i,
                                 le64_to_cpu(u0->a),
                                 le64_to_cpu(u0->b),
                                 (u64)buffer_info->dma,
@@ -3161,7 +3161,7 @@ void igb_unmap_and_free_tx_resource(struct igb_ring *tx_ring,
         }
         buffer_info->time_stamp = 0;
         buffer_info->length = 0;
-        buffer_info->next_to_watch = 0;
+        buffer_info->next_to_watch = NULL;
         buffer_info->mapped_as_page = false;
 }
 
@@ -4107,7 +4107,7 @@ static inline bool igb_tx_csum(struct igb_ring *tx_ring,
 #define IGB_MAX_DATA_PER_TXD    (1<<IGB_MAX_TXD_PWR)
 
 static inline int igb_tx_map(struct igb_ring *tx_ring, struct sk_buff *skb,
-                             unsigned int first)
+                             struct igb_tx_buffer *first)
 {
         struct igb_tx_buffer *buffer_info;
         struct device *dev = tx_ring->dev;
@@ -4121,7 +4121,6 @@ static inline int igb_tx_map(struct igb_ring *tx_ring, struct sk_buff *skb,
         buffer_info = &tx_ring->tx_buffer_info[i];
         BUG_ON(hlen >= IGB_MAX_DATA_PER_TXD);
         buffer_info->length = hlen;
-        buffer_info->next_to_watch = i;
         buffer_info->dma = dma_map_single(dev, skb->data, hlen,
                                           DMA_TO_DEVICE);
         if (dma_mapping_error(dev, buffer_info->dma))
@@ -4139,7 +4138,6 @@ static inline int igb_tx_map(struct igb_ring *tx_ring, struct sk_buff *skb,
                 buffer_info = &tx_ring->tx_buffer_info[i];
                 BUG_ON(len >= IGB_MAX_DATA_PER_TXD);
                 buffer_info->length = len;
-                buffer_info->next_to_watch = i;
                 buffer_info->mapped_as_page = true;
                 buffer_info->dma = skb_frag_dma_map(dev, frag, 0, len,
                                                 DMA_TO_DEVICE);
@@ -4153,8 +4151,12 @@ static inline int igb_tx_map(struct igb_ring *tx_ring, struct sk_buff *skb,
         /* multiply data chunks by size of headers */
         buffer_info->bytecount = ((gso_segs - 1) * hlen) + skb->len;
         buffer_info->gso_segs = gso_segs;
-        tx_ring->tx_buffer_info[first].next_to_watch = i;
-        tx_ring->tx_buffer_info[first].time_stamp = jiffies;
+
+        /* set the timestamp */
+        first->time_stamp = jiffies;
+
+        /* set next_to_watch value indicating a packet is present */
+        first->next_to_watch = IGB_TX_DESC(tx_ring, i);
 
         return ++count;
 
@@ -4165,7 +4167,6 @@ dma_error:
         buffer_info->dma = 0;
         buffer_info->time_stamp = 0;
         buffer_info->length = 0;
-        buffer_info->next_to_watch = 0;
         buffer_info->mapped_as_page = false;
 
         /* clear timestamp and dma mappings for remaining portion of packet */
@@ -4283,9 +4284,9 @@ static inline int igb_maybe_stop_tx(struct igb_ring *tx_ring, int size)
 netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
                                 struct igb_ring *tx_ring)
 {
+        struct igb_tx_buffer *first;
         int tso, count;
         u32 tx_flags = 0;
-        u16 first;
         u8 hdr_len = 0;
 
         /* need: 1 descriptor per page,
@@ -4311,7 +4312,8 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
         if (skb->protocol == htons(ETH_P_IP))
                 tx_flags |= IGB_TX_FLAGS_IPV4;
 
-        first = tx_ring->next_to_use;
+        /* record the location of the first descriptor for this packet */
+        first = &tx_ring->tx_buffer_info[tx_ring->next_to_use];
 
         tso = igb_tso(tx_ring, skb, tx_flags, &hdr_len);
 
@@ -4330,8 +4332,8 @@ netdev_tx_t igb_xmit_frame_ring(struct sk_buff *skb,
         count = igb_tx_map(tx_ring, skb, first);
         if (!count) {
                 dev_kfree_skb_any(skb);
-                tx_ring->tx_buffer_info[first].time_stamp = 0;
-                tx_ring->next_to_use = first;
+                first->time_stamp = 0;
+                tx_ring->next_to_use = first - tx_ring->tx_buffer_info;
                 return NETDEV_TX_OK;
         }
 
@@ -5568,29 +5570,34 @@ 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;
+        union e1000_adv_tx_desc *tx_desc, *eop_desc;
         unsigned int total_bytes = 0, total_packets = 0;
         unsigned int budget = q_vector->tx_work_limit;
-        u16 i = tx_ring->next_to_clean;
+        unsigned int i = tx_ring->next_to_clean;
 
         if (test_bit(__IGB_DOWN, &adapter->state))
                 return true;
 
         tx_buffer = &tx_ring->tx_buffer_info[i];
         tx_desc = IGB_TX_DESC(tx_ring, i);
+        i -= tx_ring->count;
 
         for (; budget; budget--) {
-                u16 eop = tx_buffer->next_to_watch;
-                union e1000_adv_tx_desc *eop_desc;
+                eop_desc = tx_buffer->next_to_watch;
 
-                eop_desc = IGB_TX_DESC(tx_ring, eop);
+                /* prevent any other reads prior to eop_desc */
+                rmb();
+
+                /* if next_to_watch is not set then there is no work pending */
+                if (!eop_desc)
+                        break;
 
                 /* if DD is not set pending work has not been completed */
                 if (!(eop_desc->wb.status & cpu_to_le32(E1000_TXD_STAT_DD)))
                         break;
 
-                /* prevent any other reads prior to eop_desc being verified */
-                rmb();
+                /* clear next_to_watch to prevent false hangs */
+                tx_buffer->next_to_watch = NULL;
 
                 do {
                         tx_desc->wb.status = 0;
@@ -5607,14 +5614,15 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
                         tx_buffer++;
                         tx_desc++;
                         i++;
-                        if (unlikely(i == tx_ring->count)) {
-                                i = 0;
+                        if (unlikely(!i)) {
+                                i -= tx_ring->count;
                                 tx_buffer = tx_ring->tx_buffer_info;
                                 tx_desc = IGB_TX_DESC(tx_ring, 0);
                         }
                 } while (eop_desc);
         }
 
+        i += tx_ring->count;
         tx_ring->next_to_clean = i;
         u64_stats_update_begin(&tx_ring->tx_syncp);
         tx_ring->tx_stats.bytes += total_bytes;
@@ -5625,16 +5633,14 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
 
         if (tx_ring->detect_tx_hung) {
                 struct e1000_hw *hw = &adapter->hw;
-                u16 eop = tx_ring->tx_buffer_info[i].next_to_watch;
-                union e1000_adv_tx_desc *eop_desc;
 
-                eop_desc = IGB_TX_DESC(tx_ring, eop);
+                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 */
                 tx_ring->detect_tx_hung = false;
-                if (tx_ring->tx_buffer_info[i].time_stamp &&
-                    time_after(jiffies, tx_ring->tx_buffer_info[i].time_stamp +
+                if (eop_desc &&
+                    time_after(jiffies, tx_buffer->time_stamp +
                                (adapter->tx_timeout_factor * HZ)) &&
                     !(rd32(E1000_STATUS) & E1000_STATUS_TXOFF)) {
 
@@ -5648,7 +5654,7 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
                                 "  next_to_clean        <%x>\n"
                                 "buffer_info[next_to_clean]\n"
                                 "  time_stamp           <%lx>\n"
-                                "  next_to_watch        <%x>\n"
+                                "  next_to_watch        <%p>\n"
                                 "  jiffies              <%lx>\n"
                                 "  desc.status          <%x>\n",
                                 tx_ring->queue_index,
@@ -5656,8 +5662,8 @@ static bool igb_clean_tx_irq(struct igb_q_vector *q_vector)
                                 readl(tx_ring->tail),
                                 tx_ring->next_to_use,
                                 tx_ring->next_to_clean,
-                                tx_ring->tx_buffer_info[eop].time_stamp,
-                                eop,
+                                tx_buffer->time_stamp,
+                                eop_desc,
                                 jiffies,
                                 eop_desc->wb.status);
                         netif_stop_subqueue(tx_ring->netdev,