net/mlx4_en: Improve receive data-path

Several small performance improvements in RX datapath,
including:
- Compiler branch predictor hints.
- Replace a multiplication with a shift operation.
- Minimize variables scope.
- Write-prefetch for packet header.
- Avoid trinary-operator ("?") when value can be preset in a matching
  branch.
- Save a branch by updating RX ring doorbell within
  mlx4_en_refill_rx_buffers(), which now returns void.

Performance tests:
Tested on ConnectX3Pro, Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz
Single queue no-RSS optimization ON
(enable by ethtool -L <interface> rx 1).

XDP_DROP packet rate:
Same (28.1 Mpps), lower CPU utilization (from ~100% to ~92%).

Drop packets in TC:
-------------------------------------
     | Before    | After     | Gain |
IPv4 | 4.14 Mpps | 4.18 Mpps |   1% |
-------------------------------------

XDP_TX packet rate:
-------------------------------------
     | Before    | After     | Gain |
IPv4 | 10.1 Mpps | 10.3 Mpps |   2% |
IPv6 | 10.1 Mpps | 10.3 Mpps |   2% |
-------------------------------------

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
Cc: kernel-team@fb.com
Cc: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index c4edae8..507c48e 100644 (file)
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -134,10 +134,11 @@ static int mlx4_en_prepare_rx_desc(struct mlx4_en_priv *priv,
                                   struct mlx4_en_rx_ring *ring, int index,
                                   gfp_t gfp)
 {
-       struct mlx4_en_rx_desc *rx_desc = ring->buf + (index * ring->stride);
+       struct mlx4_en_rx_desc *rx_desc = ring->buf +
+               (index << ring->log_stride);
        struct mlx4_en_rx_alloc *frags = ring->rx_info +
                                        (index << priv->log_rx_info);
-       if (ring->page_cache.index > 0) {
+       if (likely(ring->page_cache.index > 0)) {
                /* XDP uses a single page per frame */
                if (!frags->page) {
                        ring->page_cache.index--;
@@ -178,6 +179,7 @@ static void mlx4_en_free_rx_desc(const struct mlx4_en_priv *priv,
        }
 }
 
+/* Function not in fast-path */
 static int mlx4_en_fill_rx_buffers(struct mlx4_en_priv *priv)
 {
        struct mlx4_en_rx_ring *ring;
@@ -539,14 +541,14 @@ static void validate_loopback(struct mlx4_en_priv *priv, void *va)
        priv->loopback_ok = 1;
 }
 
-static bool mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
+static void mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
                                      struct mlx4_en_rx_ring *ring)
 {
        u32 missing = ring->actual_size - (ring->prod - ring->cons);
 
        /* Try to batch allocations, but not too much. */
        if (missing < 8)
-               return false;
+               return;
        do {
                if (mlx4_en_prepare_rx_desc(priv, ring,
                                            ring->prod & ring->size_mask,
@@ -554,9 +556,9 @@ static bool mlx4_en_refill_rx_buffers(struct mlx4_en_priv *priv,
                                            __GFP_MEMALLOC))
                        break;
                ring->prod++;
-       } while (--missing);
+       } while (likely(--missing));
 
-       return true;
+       mlx4_en_update_rx_prod_db(ring);
 }
 
 /* When hardware doesn't strip the vlan, we need to calculate the checksum
@@ -637,21 +639,14 @@ static int check_csum(struct mlx4_cqe *cqe, struct sk_buff *skb, void *va,
 int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int budget)
 {
        struct mlx4_en_priv *priv = netdev_priv(dev);
-       struct mlx4_en_dev *mdev = priv->mdev;
-       struct mlx4_cqe *cqe;
-       struct mlx4_en_rx_ring *ring = priv->rx_ring[cq->ring];
-       struct mlx4_en_rx_alloc *frags;
+       int factor = priv->cqe_factor;
+       struct mlx4_en_rx_ring *ring;
        struct bpf_prog *xdp_prog;
+       int cq_ring = cq->ring;
        int doorbell_pending;
-       struct sk_buff *skb;
-       int index;
-       int nr;
-       unsigned int length;
+       struct mlx4_cqe *cqe;
        int polled = 0;
-       int ip_summed;
-       int factor = priv->cqe_factor;
-       u64 timestamp;
-       bool l2_tunnel;
+       int index;
 
        if (unlikely(!priv->port_up))
                return 0;
@@ -659,6 +654,8 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
        if (unlikely(budget <= 0))
                return polled;
 
+       ring = priv->rx_ring[cq_ring];
+
        /* Protect accesses to: ring->xdp_prog, priv->mac_hash list */
        rcu_read_lock();
        xdp_prog = rcu_dereference(ring->xdp_prog);
@@ -673,10 +670,17 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
        /* Process all completed CQEs */
        while (XNOR(cqe->owner_sr_opcode & MLX4_CQE_OWNER_MASK,
                    cq->mcq.cons_index & cq->size)) {
+               struct mlx4_en_rx_alloc *frags;
+               enum pkt_hash_types hash_type;
+               struct sk_buff *skb;
+               unsigned int length;
+               int ip_summed;
                void *va;
+               int nr;
 
                frags = ring->rx_info + (index << priv->log_rx_info);
                va = page_address(frags[0].page) + frags[0].page_offset;
+               prefetchw(va);
                /*
                 * make sure we read the CQE after we read the ownership bit
                 */
@@ -768,7 +772,7 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
                                break;
                        case XDP_TX:
                                if (likely(!mlx4_en_xmit_frame(ring, frags, dev,
-                                                       length, cq->ring,
+                                                       length, cq_ring,
                                                        &doorbell_pending))) {
                                        frags[0].page = NULL;
                                        goto next;
@@ -790,24 +794,27 @@ xdp_drop_no_cnt:
                ring->packets++;
 
                skb = napi_get_frags(&cq->napi);
-               if (!skb)
+               if (unlikely(!skb))
                        goto next;
 
                if (unlikely(ring->hwtstamp_rx_filter == HWTSTAMP_FILTER_ALL)) {
-                       timestamp = mlx4_en_get_cqe_ts(cqe);
-                       mlx4_en_fill_hwtstamps(mdev, skb_hwtstamps(skb),
+                       u64 timestamp = mlx4_en_get_cqe_ts(cqe);
+
+                       mlx4_en_fill_hwtstamps(priv->mdev, skb_hwtstamps(skb),
                                               timestamp);
                }
-               skb_record_rx_queue(skb, cq->ring);
+               skb_record_rx_queue(skb, cq_ring);
 
                if (likely(dev->features & NETIF_F_RXCSUM)) {
                        if (cqe->status & cpu_to_be16(MLX4_CQE_STATUS_TCP |
                                                      MLX4_CQE_STATUS_UDP)) {
                                if ((cqe->status & cpu_to_be16(MLX4_CQE_STATUS_IPOK)) &&
                                    cqe->checksum == cpu_to_be16(0xffff)) {
-                                       ip_summed = CHECKSUM_UNNECESSARY;
-                                       l2_tunnel = (dev->hw_enc_features & NETIF_F_RXCSUM) &&
+                                       bool l2_tunnel = (dev->hw_enc_features & NETIF_F_RXCSUM) &&
                                                (cqe->vlan_my_qpn & cpu_to_be32(MLX4_CQE_L2_TUNNEL));
+
+                                       ip_summed = CHECKSUM_UNNECESSARY;
+                                       hash_type = PKT_HASH_TYPE_L4;
                                        if (l2_tunnel)
                                                skb->csum_level = 1;
                                        ring->csum_ok++;
@@ -822,6 +829,7 @@ xdp_drop_no_cnt:
                                                goto csum_none;
                                        } else {
                                                ip_summed = CHECKSUM_COMPLETE;
+                                               hash_type = PKT_HASH_TYPE_L3;
                                                ring->csum_complete++;
                                        }
                                } else {
@@ -831,16 +839,14 @@ xdp_drop_no_cnt:
                } else {
 csum_none:
                        ip_summed = CHECKSUM_NONE;
+                       hash_type = PKT_HASH_TYPE_L3;
                        ring->csum_none++;
                }
                skb->ip_summed = ip_summed;
                if (dev->features & NETIF_F_RXHASH)
                        skb_set_hash(skb,
                                     be32_to_cpu(cqe->immed_rss_invalid),
-                                    (ip_summed == CHECKSUM_UNNECESSARY) ?
-                                       PKT_HASH_TYPE_L4 :
-                                       PKT_HASH_TYPE_L3);
-
+                                    hash_type);
 
                if ((cqe->vlan_my_qpn &
                     cpu_to_be32(MLX4_CQE_CVLAN_PRESENT_MASK)) &&
@@ -867,13 +873,13 @@ next:
                ++cq->mcq.cons_index;
                index = (cq->mcq.cons_index) & ring->size_mask;
                cqe = mlx4_en_get_cqe(cq->buf, index, priv->cqe_size) + factor;
-               if (++polled == budget)
+               if (unlikely(++polled == budget))
                        break;
        }
 
        rcu_read_unlock();
 
-       if (polled) {
+       if (likely(polled)) {
                if (doorbell_pending)
                        mlx4_en_xmit_doorbell(priv->tx_ring[TX_XDP][cq->ring]);
 
@@ -883,8 +889,7 @@ next:
        }
        AVG_PERF_COUNTER(priv->pstats.rx_coal_avg, polled);
 
-       if (mlx4_en_refill_rx_buffers(priv, ring))
-               mlx4_en_update_rx_prod_db(ring);
+       mlx4_en_refill_rx_buffers(priv, ring);
 
        return polled;
 }
@@ -936,7 +941,7 @@ int mlx4_en_poll_rx_cq(struct napi_struct *napi, int budget)
                        done--;
        }
        /* Done for now */
-       if (napi_complete_done(napi, done))
+       if (likely(napi_complete_done(napi, done)))
                mlx4_en_arm_cq(priv, cq);
        return done;
 }