enic: implement rx_copybreak

Calling dma_map_single()/dma_unmap_single() is quite expensive compared
to copying a small packet. So let's copy short frames and keep the buffers
mapped.

Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 48 insertions, 3 deletions

diff --git a/drivers/net/ethernet/cisco/enic/enic.h b/drivers/net/ethernet/cisco/enic/enic.h
index 962510f391df..5ba5ad071bb6 100644
--- a/drivers/net/ethernet/cisco/enic/enic.h
+++ b/drivers/net/ethernet/cisco/enic/enic.h
@@ -186,6 +186,7 @@ struct enic {
         ____cacheline_aligned struct vnic_cq cq[ENIC_CQ_MAX];
         unsigned int cq_count;
         struct enic_rfs_flw_tbl rfs_h;
+        u32 rx_copybreak;
 };
 
 static inline struct device *enic_get_dev(struct enic *enic)
diff --git a/drivers/net/ethernet/cisco/enic/enic_main.c b/drivers/net/ethernet/cisco/enic/enic_main.c
index c8832bc1c5f7..929bfe70080a 100644
--- a/drivers/net/ethernet/cisco/enic/enic_main.c
+++ b/drivers/net/ethernet/cisco/enic/enic_main.c
@@ -66,6 +66,8 @@
 #define PCI_DEVICE_ID_CISCO_VIC_ENET_DYN     0x0044  /* enet dynamic vnic */
 #define PCI_DEVICE_ID_CISCO_VIC_ENET_VF      0x0071  /* enet SRIOV VF */
 
+#define RX_COPYBREAK_DEFAULT            256
+
 /* Supported devices */
 static const struct pci_device_id enic_id_table[] = {
         { PCI_VDEVICE(CISCO, PCI_DEVICE_ID_CISCO_VIC_ENET) },
@@ -924,6 +926,7 @@ static void enic_free_rq_buf(struct vnic_rq *rq, struct vnic_rq_buf *buf)
         pci_unmap_single(enic->pdev, buf->dma_addr,
                 buf->len, PCI_DMA_FROMDEVICE);
         dev_kfree_skb_any(buf->os_buf);
+        buf->os_buf = NULL;
 }
 
 static int enic_rq_alloc_buf(struct vnic_rq *rq)
@@ -934,7 +937,24 @@ static int enic_rq_alloc_buf(struct vnic_rq *rq)
         unsigned int len = netdev->mtu + VLAN_ETH_HLEN;
         unsigned int os_buf_index = 0;
         dma_addr_t dma_addr;
+        struct vnic_rq_buf *buf = rq->to_use;
+
+        if (buf->os_buf) {
+                buf = buf->next;
+                rq->to_use = buf;
+                rq->ring.desc_avail--;
+                if ((buf->index & VNIC_RQ_RETURN_RATE) == 0) {
+                        /* Adding write memory barrier prevents compiler and/or
+                         * CPU reordering, thus avoiding descriptor posting
+                         * before descriptor is initialized. Otherwise, hardware
+                         * can read stale descriptor fields.
+                         */
+                        wmb();
+                        iowrite32(buf->index, &rq->ctrl->posted_index);
+                }
 
+                return 0;
+        }
         skb = netdev_alloc_skb_ip_align(netdev, len);
         if (!skb)
                 return -ENOMEM;
@@ -957,6 +977,25 @@ static void enic_intr_update_pkt_size(struct vnic_rx_bytes_counter *pkt_size,
                 pkt_size->small_pkt_bytes_cnt += pkt_len;
 }
 
+static bool enic_rxcopybreak(struct net_device *netdev, struct sk_buff **skb,
+                             struct vnic_rq_buf *buf, u16 len)
+{
+        struct enic *enic = netdev_priv(netdev);
+        struct sk_buff *new_skb;
+
+        if (len > enic->rx_copybreak)
+                return false;
+        new_skb = netdev_alloc_skb_ip_align(netdev, len);
+        if (!new_skb)
+                return false;
+        pci_dma_sync_single_for_cpu(enic->pdev, buf->dma_addr, len,
+                                    DMA_FROM_DEVICE);
+        memcpy(new_skb->data, (*skb)->data, len);
+        *skb = new_skb;
+
+        return true;
+}
+
 static void enic_rq_indicate_buf(struct vnic_rq *rq,
         struct cq_desc *cq_desc, struct vnic_rq_buf *buf,
         int skipped, void *opaque)
@@ -978,9 +1017,6 @@ static void enic_rq_indicate_buf(struct vnic_rq *rq,
                 return;
 
         skb = buf->os_buf;
-        prefetch(skb->data - NET_IP_ALIGN);
-        pci_unmap_single(enic->pdev, buf->dma_addr,
-                buf->len, PCI_DMA_FROMDEVICE);
 
         cq_enet_rq_desc_dec((struct cq_enet_rq_desc *)cq_desc,
                 &type, &color, &q_number, &completed_index,
@@ -1011,6 +1047,13 @@ static void enic_rq_indicate_buf(struct vnic_rq *rq,
                 /* Good receive
                  */
 
+                if (!enic_rxcopybreak(netdev, &skb, buf, bytes_written)) {
+                        buf->os_buf = NULL;
+                        pci_unmap_single(enic->pdev, buf->dma_addr, buf->len,
+                                         PCI_DMA_FROMDEVICE);
+                }
+                prefetch(skb->data - NET_IP_ALIGN);
+
                 skb_put(skb, bytes_written);
                 skb->protocol = eth_type_trans(skb, netdev);
                 skb_record_rx_queue(skb, q_number);
@@ -2531,6 +2574,7 @@ static int enic_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
                 dev_err(dev, "Cannot register net device, aborting\n");
                 goto err_out_dev_deinit;
         }
+        enic->rx_copybreak = RX_COPYBREAK_DEFAULT;
 
         return 0;