ixgbe: delay tail write to every 'n' packets

Current XDP implementation hits the tail on every XDP_TX return
code. This patch changes driver behavior to only hit the tail after
packet processing is complete.

With this patch I can run XDP drop programs @ 14+Mpps and XDP_TX
programs are at ~13.5Mpps.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index cb5be7d..3d7b091 100644 (file)
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -2283,6 +2283,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
        unsigned int mss = 0;
 #endif /* IXGBE_FCOE */
        u16 cleaned_count = ixgbe_desc_unused(rx_ring);
+       bool xdp_xmit = false;
 
        while (likely(total_rx_packets < budget)) {
                union ixgbe_adv_rx_desc *rx_desc;
@@ -2322,10 +2323,12 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
                }
 
                if (IS_ERR(skb)) {
-                       if (PTR_ERR(skb) == -IXGBE_XDP_TX)
+                       if (PTR_ERR(skb) == -IXGBE_XDP_TX) {
+                               xdp_xmit = true;
                                ixgbe_rx_buffer_flip(rx_ring, rx_buffer, size);
-                       else
+                       } else {
                                rx_buffer->pagecnt_bias++;
+                       }
                        total_rx_packets++;
                        total_rx_bytes += size;
                } else if (skb) {
@@ -2393,6 +2396,16 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
                total_rx_packets++;
        }
 
+       if (xdp_xmit) {
+               struct ixgbe_ring *ring = adapter->xdp_ring[smp_processor_id()];
+
+               /* Force memory writes to complete before letting h/w
+                * know there are new descriptors to fetch.
+                */
+               wmb();
+               writel(ring->next_to_use, ring->tail);
+       }
+
        u64_stats_update_begin(&rx_ring->syncp);
        rx_ring->stats.packets += total_rx_packets;
        rx_ring->stats.bytes += total_rx_bytes;
@@ -8238,14 +8251,8 @@ static int ixgbe_xmit_xdp_ring(struct ixgbe_adapter *adapter,
        tx_desc->read.olinfo_status =
                cpu_to_le32(len << IXGBE_ADVTXD_PAYLEN_SHIFT);
 
-       /* Force memory writes to complete before letting h/w know there
-        * are new descriptors to fetch.  (Only applicable for weak-ordered
-        * memory model archs, such as IA-64).
-        *
-        * We also need this memory barrier to make certain all of the
-        * status bits have been updated before next_to_watch is written.
-        */
-       wmb();
+       /* Avoid any potential race with xdp_xmit and cleanup */
+       smp_wmb();
 
        /* set next_to_watch value indicating a packet is present */
        i++;
@@ -8255,7 +8262,6 @@ static int ixgbe_xmit_xdp_ring(struct ixgbe_adapter *adapter,
        tx_buffer->next_to_watch = tx_desc;
        ring->next_to_use = i;
 
-       writel(i, ring->tail);
        return IXGBE_XDP_TX;
 }