vxge: prefetch skb->data

This patch implements prefetching of skb->data from a copy of the pointer
in the descriptor (which is already in the L1 cache at this point).  This
improves netperf rx performance (netperf -L 0,0 -c -H 192.168.254.2 -- -M
131072 -m 131072) by 4.9% on a P4 Xeon host.

Signed-off-by: Benjamin LaHaise <ben.lahaise@neterion.com>
Signed-off-by: Sreenivasa Honnur <sreenivasa.honnur@neterion.com>
Signed-off-by: Ramkrishna Vepa <ram.vepa@neterion.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 6 insertions, 1 deletions

diff --git a/drivers/net/vxge/vxge-main.c b/drivers/net/vxge/vxge-main.c
index e93651c19f59..094d15548a2b 100644
--- a/drivers/net/vxge/vxge-main.c
+++ b/drivers/net/vxge/vxge-main.c
@@ -286,6 +286,7 @@ vxge_rx_alloc(void *dtrh, struct vxge_ring *ring, const int skb_size)
         skb_reserve(skb, VXGE_HW_HEADER_ETHERNET_II_802_3_ALIGN);
 
         rx_priv->skb = skb;
+        rx_priv->skb_data = NULL;
         rx_priv->data_size = skb_size;
         vxge_debug_entryexit(VXGE_TRACE,
                 "%s: %s:%d Exiting...", ring->ndev->name, __func__, __LINE__);
@@ -305,7 +306,8 @@ static int vxge_rx_map(void *dtrh, struct vxge_ring *ring)
                 ring->ndev->name, __func__, __LINE__);
         rx_priv = vxge_hw_ring_rxd_private_get(dtrh);
 
-        dma_addr = pci_map_single(ring->pdev, rx_priv->skb->data,
+        rx_priv->skb_data = rx_priv->skb->data;
+        dma_addr = pci_map_single(ring->pdev, rx_priv->skb_data,
                                 rx_priv->data_size, PCI_DMA_FROMDEVICE);
 
         if (dma_addr == 0) {
@@ -450,6 +452,7 @@ vxge_rx_1b_compl(struct __vxge_hw_ring *ringh, void *dtr,
                 skb = rx_priv->skb;
                 data_size = rx_priv->data_size;
                 data_dma = rx_priv->data_dma;
+                prefetch(rx_priv->skb_data);
 
                 vxge_debug_rx(VXGE_TRACE,
                         "%s: %s:%d  skb = 0x%p",
@@ -1056,6 +1059,7 @@ vxge_rx_term(void *dtrh, enum vxge_hw_rxd_state state, void *userdata)
                 rx_priv->data_size, PCI_DMA_FROMDEVICE);
 
         dev_kfree_skb(rx_priv->skb);
+        rx_priv->skb_data = NULL;
 
         vxge_debug_entryexit(VXGE_TRACE,
                 "%s: %s:%d  Exiting...",
diff --git a/drivers/net/vxge/vxge-main.h b/drivers/net/vxge/vxge-main.h
index 8b3989bc707f..9c36b3a9a63d 100644
--- a/drivers/net/vxge/vxge-main.h
+++ b/drivers/net/vxge/vxge-main.h
@@ -378,6 +378,7 @@ struct vxgedev {
 
 struct vxge_rx_priv {
         struct sk_buff          *skb;
+        unsigned char           *skb_data;
         dma_addr_t              data_dma;
         dma_addr_t              data_size;
 };