mlx4_en: optimize adaptive moderation algorithm for better latency
Yevgeny Petrilin [Tue, 22 Mar 2011 22:37:36 +0000 (22:37 +0000)]
Signed-off-by: Yevgeny Petrilin <yevgenyp@mellanox.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/mlx4/en_netdev.c
drivers/net/mlx4/mlx4_en.h

index 56627c2..b1180dd 100644 (file)
@@ -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",
index dfed6a0..5387c4e 100644 (file)
@@ -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