ice: add build_skb() support

Driver is now prepared for building the skb around the existing Rx
buffer, so introduce the ice_build_skb responsible for it. Make use of
XDP's data_meta as well.

I've observed around 30% less CPU consumption with build_skb Rx path, in
comparison to legacy Rx. What stands behind such result is the avoidance
of flow_dissector (which we were diving into via eth_get_headlen) and no
memcpy calls.

Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@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/ice/ice_txrx.c b/drivers/net/ethernet/intel/ice/ice_txrx.c
index bd1f73af468c8eff9ea6123cadc256aae062204a..40a29b9d30346bfe75f1711436e2c941013369b6 100644 (file)
--- a/drivers/net/ethernet/intel/ice/ice_txrx.c
+++ b/drivers/net/ethernet/intel/ice/ice_txrx.c
@@ -790,6 +790,60 @@ ice_get_rx_buf(struct ice_ring *rx_ring, struct sk_buff **skb,
        return rx_buf;
 }
 
+/**
+ * ice_build_skb - Build skb around an existing buffer
+ * @rx_ring: Rx descriptor ring to transact packets on
+ * @rx_buf: Rx buffer to pull data from
+ * @xdp: xdp_buff pointing to the data
+ *
+ * This function builds an skb around an existing Rx buffer, taking care
+ * to set up the skb correctly and avoid any memcpy overhead.
+ */
+static struct sk_buff *
+ice_build_skb(struct ice_ring *rx_ring, struct ice_rx_buf *rx_buf,
+             struct xdp_buff *xdp)
+{
+       unsigned int metasize = xdp->data - xdp->data_meta;
+#if (PAGE_SIZE < 8192)
+       unsigned int truesize = ice_rx_pg_size(rx_ring) / 2;
+#else
+       unsigned int truesize = SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) +
+                               SKB_DATA_ALIGN(xdp->data_end -
+                                              xdp->data_hard_start);
+#endif
+       struct sk_buff *skb;
+
+       /* Prefetch first cache line of first page. If xdp->data_meta
+        * is unused, this points exactly as xdp->data, otherwise we
+        * likely have a consumer accessing first few bytes of meta
+        * data, and then actual data.
+        */
+       prefetch(xdp->data_meta);
+#if L1_CACHE_BYTES < 128
+       prefetch((void *)(xdp->data + L1_CACHE_BYTES));
+#endif
+       /* build an skb around the page buffer */
+       skb = build_skb(xdp->data_hard_start, truesize);
+       if (unlikely(!skb))
+               return NULL;
+
+       /* must to record Rx queue, otherwise OS features such as
+        * symmetric queue won't work
+        */
+       skb_record_rx_queue(skb, rx_ring->q_index);
+
+       /* update pointers within the skb to store the data */
+       skb_reserve(skb, xdp->data - xdp->data_hard_start);
+       __skb_put(skb, xdp->data_end - xdp->data);
+       if (metasize)
+               skb_metadata_set(skb, metasize);
+
+       /* buffer is used by skb, update page_offset */
+       ice_rx_buf_adjust_pg_offset(rx_buf, truesize);
+
+       return skb;
+}
+
 /**
  * ice_construct_skb - Allocate skb and populate it
  * @rx_ring: Rx descriptor ring to transact packets on
@@ -996,12 +1050,14 @@ static int ice_clean_rx_irq(struct ice_ring *rx_ring, int budget)
                if (!size) {
                        xdp.data = NULL;
                        xdp.data_end = NULL;
+                       xdp.data_hard_start = NULL;
+                       xdp.data_meta = NULL;
                        goto construct_skb;
                }
 
                xdp.data = page_address(rx_buf->page) + rx_buf->page_offset;
                xdp.data_hard_start = xdp.data - ice_rx_offset(rx_ring);
-               xdp_set_data_meta_invalid(&xdp);
+               xdp.data_meta = xdp.data;
                xdp.data_end = xdp.data + size;
 
                rcu_read_lock();
@@ -1038,6 +1094,8 @@ static int ice_clean_rx_irq(struct ice_ring *rx_ring, int budget)
 construct_skb:
                if (skb)
                        ice_add_rx_frag(rx_ring, rx_buf, skb, size);
+               else if (ice_ring_uses_build_skb(rx_ring))
+                       skb = ice_build_skb(rx_ring, rx_buf, &xdp);
                else
                        skb = ice_construct_skb(rx_ring, rx_buf, &xdp);