ibmveth: Add tx_copybreak

Use the existing bounce buffer if we send a buffer under a certain size.
This saves the overhead of a TCE map/unmap.

I can't see any reason for the wmb() in the bounce buffer case, if we need
a barrier it will be before we call h_send_logical_lan but we have
nothing in the common case. Remove it.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Santiago Leon <santil@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 20 insertions, 8 deletions

diff --git a/drivers/net/ibmveth.c b/drivers/net/ibmveth.c
index 9d662dec21b0..fc6e2cf879c0 100644
--- a/drivers/net/ibmveth.c
+++ b/drivers/net/ibmveth.c
@@ -117,6 +117,11 @@ MODULE_DESCRIPTION("IBM i/pSeries Virtual Ethernet Driver");
 MODULE_LICENSE("GPL");
 MODULE_VERSION(ibmveth_driver_version);
 
+static unsigned int tx_copybreak __read_mostly = 128;
+module_param(tx_copybreak, uint, 0644);
+MODULE_PARM_DESC(tx_copybreak,
+        "Maximum size of packet that is copied to a new buffer on transmit");
+
 struct ibmveth_stat {
         char name[ETH_GSTRING_LEN];
         int offset;
@@ -931,17 +936,24 @@ static netdev_tx_t ibmveth_start_xmit(struct sk_buff *skb,
                 buf[1] = 0;
         }
 
-        data_dma_addr = dma_map_single(&adapter->vdev->dev, skb->data,
-                                       skb->len, DMA_TO_DEVICE);
-        if (dma_mapping_error(&adapter->vdev->dev, data_dma_addr)) {
-                if (!firmware_has_feature(FW_FEATURE_CMO))
-                        ibmveth_error_printk("tx: unable to map xmit buffer\n");
+        if (skb->len < tx_copybreak) {
+                used_bounce = 1;
+        } else {
+                data_dma_addr = dma_map_single(&adapter->vdev->dev, skb->data,
+                                               skb->len, DMA_TO_DEVICE);
+                if (dma_mapping_error(&adapter->vdev->dev, data_dma_addr)) {
+                        if (!firmware_has_feature(FW_FEATURE_CMO))
+                                ibmveth_error_printk("tx: unable to map "
+                                                     "xmit buffer\n");
+                        tx_map_failed++;
+                        used_bounce = 1;
+                }
+        }
+
+        if (used_bounce) {
                 skb_copy_from_linear_data(skb, adapter->bounce_buffer,
                                           skb->len);
                 desc.fields.address = adapter->bounce_buffer_dma;
-                tx_map_failed++;
-                used_bounce = 1;
-                wmb();
         } else
                 desc.fields.address = data_dma_addr;