net: socionext: Use descriptor info instead of MMIO reads on Rx

MMIO reads for remaining packets in queue occur (at least)twice per
invocation of netsec_process_rx(). We can use the packet descriptor to
identify if it's owned by the hardware and break out, avoiding the more
expensive MMIO read operations. This has a ~2% increase on the pps of the
Rx path when tested with 64byte packets

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/socionext/netsec.c b/drivers/net/ethernet/socionext/netsec.c
index 01589b6982e4d433d4936a4bb6fa2c2510d278c0..334b6189b0118a7aba95ee55a96f0ef7961c6625 100644 (file)
--- a/drivers/net/ethernet/socionext/netsec.c
+++ b/drivers/net/ethernet/socionext/netsec.c
@@ -642,8 +642,6 @@ static struct sk_buff *netsec_get_rx_pkt_data(struct netsec_priv *priv,
 
        tmp_skb = netsec_alloc_skb(priv, &td);
 
-       dma_rmb();
-
        tail = dring->tail;
 
        if (!tmp_skb) {
@@ -657,8 +655,6 @@ static struct sk_buff *netsec_get_rx_pkt_data(struct netsec_priv *priv,
        /* move tail ahead */
        dring->tail = (dring->tail + 1) % DESC_NUM;
 
-       dring->pkt_cnt--;
-
        return skb;
 }
 
@@ -731,25 +727,24 @@ static int netsec_process_rx(struct netsec_priv *priv, int budget)
        struct netsec_desc_ring *dring = &priv->desc_ring[NETSEC_RING_RX];
        struct net_device *ndev = priv->ndev;
        struct netsec_rx_pkt_info rx_info;
-       int done = 0, rx_num = 0;
+       int done = 0;
        struct netsec_desc desc;
        struct sk_buff *skb;
        u16 len;
 
        while (done < budget) {
-               if (!rx_num) {
-                       rx_num = netsec_read(priv, NETSEC_REG_NRM_RX_PKTCNT);
-                       dring->pkt_cnt += rx_num;
+               u16 idx = dring->tail;
+               struct netsec_de *de = dring->vaddr + (DESC_SZ * idx);
 
-                       /* move head 'rx_num' */
-                       dring->head = (dring->head + rx_num) % DESC_NUM;
+               if (de->attr & (1U << NETSEC_RX_PKT_OWN_FIELD))
+                       break;
 
-                       rx_num = dring->pkt_cnt;
-                       if (!rx_num)
-                               break;
-               }
+               /* This  barrier is needed to keep us from reading
+                * any other fields out of the netsec_de until we have
+                * verified the descriptor has been written back
+                */
+               dma_rmb();
                done++;
-               rx_num--;
                skb = netsec_get_rx_pkt_data(priv, &rx_info, &desc, &len);
                if (unlikely(!skb) || rx_info.err_flag) {
                        netif_err(priv, drv, priv->ndev,