pasemi_mac: SKB unmap optimization

pasemi_mac: SKB unmap optimization

Avoid touching skb_shinfo() in the unmap path, since it turns out to
normally cause cache misses and delays. instead, save number of fragments
in the TX_RING_INFO structures since that's all that's needed anyway.

Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

1 files changed, 25 insertions, 14 deletions

diff --git a/drivers/net/pasemi_mac.c b/drivers/net/pasemi_mac.c
index 98b639742680..ca773580cc51 100644
--- a/drivers/net/pasemi_mac.c
+++ b/drivers/net/pasemi_mac.c
@@ -253,11 +253,11 @@ static int get_skb_hdr(struct sk_buff *skb, void **iphdr,
 }
 
 static int pasemi_mac_unmap_tx_skb(struct pasemi_mac *mac,
+                                    const int nfrags,
                                     struct sk_buff *skb,
                                     const dma_addr_t *dmas)
 {
         int f;
-        int nfrags = skb_shinfo(skb)->nr_frags;
         struct pci_dev *pdev = mac->dma_pdev;
 
         pci_unmap_single(pdev, dmas[0], skb_headlen(skb), PCI_DMA_TODEVICE);
@@ -425,7 +425,7 @@ static void pasemi_mac_free_tx_resources(struct pasemi_mac *mac)
         unsigned int i, j;
         struct pasemi_mac_buffer *info;
         dma_addr_t dmas[MAX_SKB_FRAGS+1];
-        int freed;
+        int freed, nfrags;
         int start, limit;
 
         start = txring->next_to_clean;
@@ -438,10 +438,12 @@ static void pasemi_mac_free_tx_resources(struct pasemi_mac *mac)
         for (i = start; i < limit; i += freed) {
                 info = &txring->ring_info[(i+1) & (TX_RING_SIZE-1)];
                 if (info->dma && info->skb) {
-                        for (j = 0; j <= skb_shinfo(info->skb)->nr_frags; j++)
+                        nfrags = skb_shinfo(info->skb)->nr_frags;
+                        for (j = 0; j <= nfrags; j++)
                                 dmas[j] = txring->ring_info[(i+1+j) &
                                                 (TX_RING_SIZE-1)].dma;
-                        freed = pasemi_mac_unmap_tx_skb(mac, info->skb, dmas);
+                        freed = pasemi_mac_unmap_tx_skb(mac, nfrags,
+                                                        info->skb, dmas);
                 } else
                         freed = 2;
         }
@@ -749,6 +751,8 @@ static int pasemi_mac_clean_tx(struct pasemi_mac_txring *txring)
         unsigned long flags;
         struct sk_buff *skbs[TX_CLEAN_BATCHSIZE];
         dma_addr_t dmas[TX_CLEAN_BATCHSIZE][MAX_SKB_FRAGS+1];
+        int nf[TX_CLEAN_BATCHSIZE];
+        int nr_frags;
 
         total_count = 0;
         batch_limit = TX_CLEAN_BATCHSIZE;
@@ -758,6 +762,8 @@ restart:
         start = txring->next_to_clean;
         ring_limit = txring->next_to_fill;
 
+        prefetch(&TX_DESC_INFO(txring, start+1).skb);
+
         /* Compensate for when fill has wrapped but clean has not */
         if (start > ring_limit)
                 ring_limit += TX_RING_SIZE;
@@ -771,6 +777,9 @@ restart:
                 u64 mactx = TX_DESC(txring, i);
                 struct sk_buff *skb;
 
+                skb = TX_DESC_INFO(txring, i+1).skb;
+                nr_frags = TX_DESC_INFO(txring, i).dma;
+
                 if ((mactx  & XCT_MACTX_E) ||
                     (*chan->status & PAS_STATUS_ERROR))
                         pasemi_mac_tx_error(mac, mactx);
@@ -779,21 +788,22 @@ restart:
                         /* Not yet transmitted */
                         break;
 
-                skb = TX_DESC_INFO(txring, i+1).skb;
-                skbs[descr_count] = skb;
+                buf_count = 2 + nr_frags;
+                /* Since we always fill with an even number of entries, make
+                 * sure we skip any unused one at the end as well.
+                 */
+                if (buf_count & 1)
+                        buf_count++;
 
-                buf_count = 2 + skb_shinfo(skb)->nr_frags;
-                for (j = 0; j <= skb_shinfo(skb)->nr_frags; j++)
+                for (j = 0; j <= nr_frags; j++)
                         dmas[descr_count][j] = TX_DESC_INFO(txring, i+1+j).dma;
 
+                skbs[descr_count] = skb;
+                nf[descr_count] = nr_frags;
+
                 TX_DESC(txring, i) = 0;
                 TX_DESC(txring, i+1) = 0;
 
-                /* Since we always fill with an even number of entries, make
-                 * sure we skip any unused one at the end as well.
-                 */
-                if (buf_count & 1)
-                        buf_count++;
                 descr_count++;
         }
         txring->next_to_clean = i & (TX_RING_SIZE-1);
@@ -802,7 +812,7 @@ restart:
         netif_wake_queue(mac->netdev);
 
         for (i = 0; i < descr_count; i++)
-                pasemi_mac_unmap_tx_skb(mac, skbs[i], dmas[i]);
+                pasemi_mac_unmap_tx_skb(mac, nf[i], skbs[i], dmas[i]);
 
         total_count += descr_count;
 
@@ -1299,6 +1309,7 @@ static int pasemi_mac_start_tx(struct sk_buff *skb, struct net_device *dev)
         }
 
         TX_DESC(txring, fill) = mactx;
+        TX_DESC_INFO(txring, fill).dma = nfrags;
         fill++;
         TX_DESC_INFO(txring, fill).skb = skb;
         for (i = 0; i <= nfrags; i++) {