mlx4_en: optimize adaptive moderation algorithm for better latency

Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 6 insertions, 13 deletions

diff --git a/drivers/net/mlx4/en_netdev.c b/drivers/net/mlx4/en_netdev.c
index 56627c26d918..b1180dd5e173 100644
--- a/drivers/net/mlx4/en_netdev.c
+++ b/drivers/net/mlx4/en_netdev.c
@@ -417,7 +417,6 @@ static void mlx4_en_auto_moderation(struct mlx4_en_priv *priv)
         unsigned long avg_pkt_size;
         unsigned long rx_packets;
         unsigned long rx_bytes;
-        unsigned long rx_byte_diff;
         unsigned long tx_packets;
         unsigned long tx_pkt_diff;
         unsigned long rx_pkt_diff;
@@ -441,25 +440,20 @@ static void mlx4_en_auto_moderation(struct mlx4_en_priv *priv)
         rx_pkt_diff = ((unsigned long) (rx_packets -
                                         priv->last_moder_packets));
         packets = max(tx_pkt_diff, rx_pkt_diff);
-        rx_byte_diff = rx_bytes - priv->last_moder_bytes;
-        rx_byte_diff = rx_byte_diff ? rx_byte_diff : 1;
         rate = packets * HZ / period;
         avg_pkt_size = packets ? ((unsigned long) (rx_bytes -
                                  priv->last_moder_bytes)) / packets : 0;
 
         /* Apply auto-moderation only when packet rate exceeds a rate that
          * it matters */
-        if (rate > MLX4_EN_RX_RATE_THRESH) {
+        if (rate > MLX4_EN_RX_RATE_THRESH && avg_pkt_size > MLX4_EN_AVG_PKT_SMALL) {
                 /* If tx and rx packet rates are not balanced, assume that
                  * traffic is mainly BW bound and apply maximum moderation.
                  * Otherwise, moderate according to packet rate */
-                if (2 * tx_pkt_diff > 3 * rx_pkt_diff &&
-                    rx_pkt_diff / rx_byte_diff <
-                    MLX4_EN_SMALL_PKT_SIZE)
-                        moder_time = priv->rx_usecs_low;
-                else if (2 * rx_pkt_diff > 3 * tx_pkt_diff)
+                if (2 * tx_pkt_diff > 3 * rx_pkt_diff ||
+                    2 * rx_pkt_diff > 3 * tx_pkt_diff) {
                         moder_time = priv->rx_usecs_high;
-                else {
+                } else {
                         if (rate < priv->pkt_rate_low)
                                 moder_time = priv->rx_usecs_low;
                         else if (rate > priv->pkt_rate_high)
@@ -471,9 +465,7 @@ static void mlx4_en_auto_moderation(struct mlx4_en_priv *priv)
                                         priv->rx_usecs_low;
                 }
         } else {
-                /* When packet rate is low, use default moderation rather than
-                 * 0 to prevent interrupt storms if traffic suddenly increases */
-                moder_time = priv->rx_usecs;
+                moder_time = priv->rx_usecs_low;
         }
 
         en_dbg(INTR, priv, "tx rate:%lu rx_rate:%lu\n",
diff --git a/drivers/net/mlx4/mlx4_en.h b/drivers/net/mlx4/mlx4_en.h
index dfed6a07c2d7..5387c4e9f295 100644
--- a/drivers/net/mlx4/mlx4_en.h
+++ b/drivers/net/mlx4/mlx4_en.h
@@ -124,6 +124,7 @@ enum {
 #define MLX4_EN_RX_SIZE_THRESH          1024
 #define MLX4_EN_RX_RATE_THRESH          (1000000 / MLX4_EN_RX_COAL_TIME_HIGH)
 #define MLX4_EN_SAMPLE_INTERVAL         0
+#define MLX4_EN_AVG_PKT_SMALL           256
 
 #define MLX4_EN_AUTO_CONF       0xffff