net/mlx4_en: Ignore budget on TX napi polling

It is recommended that TX work not count against the quota.
The cost of TX packet liberation is a minute percentage of what it costs to
process an RX frame. Furthermore, that SKB freeing makes memory available for
other paths in the stack.

Give the TX a larger budget and be more aggressive about cleaning up the Tx
descriptors this budget could be changed using ethtool:
$ ethtool -C eth1 tx-frames-irq <budget>

Signed-off-by: Amir Vadai <amirv@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

4 files changed, 24 insertions, 15 deletions

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c b/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
index fa1a069e14e6..68d763d2d030 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
@@ -417,6 +417,8 @@ static int mlx4_en_get_coalesce(struct net_device *dev,
 
         coal->tx_coalesce_usecs = priv->tx_usecs;
         coal->tx_max_coalesced_frames = priv->tx_frames;
+        coal->tx_max_coalesced_frames_irq = priv->tx_work_limit;
+
         coal->rx_coalesce_usecs = priv->rx_usecs;
         coal->rx_max_coalesced_frames = priv->rx_frames;
 
@@ -426,6 +428,7 @@ static int mlx4_en_get_coalesce(struct net_device *dev,
         coal->rx_coalesce_usecs_high = priv->rx_usecs_high;
         coal->rate_sample_interval = priv->sample_interval;
         coal->use_adaptive_rx_coalesce = priv->adaptive_rx_coal;
+
         return 0;
 }
 
@@ -434,6 +437,9 @@ static int mlx4_en_set_coalesce(struct net_device *dev,
 {
         struct mlx4_en_priv *priv = netdev_priv(dev);
 
+        if (!coal->tx_max_coalesced_frames_irq)
+                return -EINVAL;
+
         priv->rx_frames = (coal->rx_max_coalesced_frames ==
                            MLX4_EN_AUTO_CONF) ?
                                 MLX4_EN_RX_COAL_TARGET :
@@ -457,6 +463,7 @@ static int mlx4_en_set_coalesce(struct net_device *dev,
         priv->rx_usecs_high = coal->rx_coalesce_usecs_high;
         priv->sample_interval = coal->rate_sample_interval;
         priv->adaptive_rx_coal = coal->use_adaptive_rx_coalesce;
+        priv->tx_work_limit = coal->tx_max_coalesced_frames_irq;
 
         return mlx4_en_moderation_update(priv);
 }
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
index e94d96f0ef55..7345c43b019e 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
@@ -2473,6 +2473,7 @@ int mlx4_en_init_netdev(struct mlx4_en_dev *mdev, int port,
                         MLX4_WQE_CTRL_SOLICITED);
         priv->num_tx_rings_p_up = mdev->profile.num_tx_rings_p_up;
         priv->tx_ring_num = prof->tx_ring_num;
+        priv->tx_work_limit = MLX4_EN_DEFAULT_TX_WORK;
 
         priv->tx_ring = kzalloc(sizeof(struct mlx4_en_tx_ring *) * MAX_TX_RINGS,
                                 GFP_KERNEL);
diff --git a/drivers/net/ethernet/mellanox/mlx4/en_tx.c b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
index ac3dead3792c..5045bab59633 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_tx.c
@@ -351,9 +351,8 @@ int mlx4_en_free_tx_buf(struct net_device *dev, struct mlx4_en_tx_ring *ring)
         return cnt;
 }
 
-static int mlx4_en_process_tx_cq(struct net_device *dev,
-                                 struct mlx4_en_cq *cq,
-                                 int budget)
+static bool mlx4_en_process_tx_cq(struct net_device *dev,
+                                 struct mlx4_en_cq *cq)
 {
         struct mlx4_en_priv *priv = netdev_priv(dev);
         struct mlx4_cq *mcq = &cq->mcq;
@@ -372,9 +371,10 @@ static int mlx4_en_process_tx_cq(struct net_device *dev,
         int factor = priv->cqe_factor;
         u64 timestamp = 0;
         int done = 0;
+        int budget = priv->tx_work_limit;
 
         if (!priv->port_up)
-                return 0;
+                return true;
 
         index = cons_index & size_mask;
         cqe = &buf[(index << factor) + factor];
@@ -447,7 +447,7 @@ static int mlx4_en_process_tx_cq(struct net_device *dev,
                 netif_tx_wake_queue(ring->tx_queue);
                 ring->wake_queue++;
         }
-        return done;
+        return done < budget;
 }
 
 void mlx4_en_tx_irq(struct mlx4_cq *mcq)
@@ -467,18 +467,16 @@ int mlx4_en_poll_tx_cq(struct napi_struct *napi, int budget)
         struct mlx4_en_cq *cq = container_of(napi, struct mlx4_en_cq, napi);
         struct net_device *dev = cq->dev;
         struct mlx4_en_priv *priv = netdev_priv(dev);
-        int done;
+        int clean_complete;
 
-        done = mlx4_en_process_tx_cq(dev, cq, budget);
+        clean_complete = mlx4_en_process_tx_cq(dev, cq);
+        if (!clean_complete)
+                return budget;
 
-        /* If we used up all the quota - we're probably not done yet... */
-        if (done < budget) {
-                /* Done for now */
-                napi_complete(napi);
-                mlx4_en_arm_cq(priv, cq);
-                return done;
-        }
-        return budget;
+        napi_complete(napi);
+        mlx4_en_arm_cq(priv, cq);
+
+        return 0;
 }
 
 static struct mlx4_en_tx_desc *mlx4_en_bounce_to_desc(struct mlx4_en_priv *priv,
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index 624e1939e9ee..d72a5a894fc6 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -126,6 +126,8 @@ enum {
 #define MAX_TX_RINGS                    (MLX4_EN_MAX_TX_RING_P_UP * \
                                          MLX4_EN_NUM_UP)
 
+#define MLX4_EN_DEFAULT_TX_WORK         256
+
 /* Target number of packets to coalesce with interrupt moderation */
 #define MLX4_EN_RX_COAL_TARGET  44
 #define MLX4_EN_RX_COAL_TIME    0x10
@@ -543,6 +545,7 @@ struct mlx4_en_priv {
         __be32 ctrl_flags;
         u32 flags;
         u8 num_tx_rings_p_up;
+        u32 tx_work_limit;
         u32 tx_ring_num;
         u32 rx_ring_num;
         u32 rx_skb_size;