netdev - [PATCH net-next] mlx4: change TX coalescing defaults

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Message-ID: <1352168442.3140.32.camel@edumazet-glaptop>
Date:	Mon, 05 Nov 2012 18:20:42 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>,
	Yevgeny Petrilin <yevgenyp@...lanox.com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Vimalkumar <j.vimal@...il.com>
Subject: [PATCH net-next] mlx4: change TX coalescing defaults

From: Eric Dumazet <edumazet@...gle.com>

mlx4 currently uses a too high tx coalescing setting, deferring
TX completion interrupts by up to 128 us.

With the recent skb_orphan() removal in commit 8112ec3b872,
performance of a single TCP flow is capped to ~4 Gbps, unless
we increase tcp_limit_output_bytes.

I suggest using 16 us instead of 128 us, allowing a finer control.

Performance of a single TCP flow is restored to previous levels,
while keeping TCP small queues fully enabled with default sysctl.

This patch is also a BQL prereq.

Reported-by: Vimalkumar <j.vimal@...il.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Cc: Yevgeny Petrilin <yevgenyp@...lanox.com>
Cc: Or Gerlitz <ogerlitz@...lanox.com>
---
By the way, is BQL addition planned for this driver ?

 drivers/net/ethernet/mellanox/mlx4/en_netdev.c |    2 +-
 drivers/net/ethernet/mellanox/mlx4/mlx4_en.h   |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
index edd9cb8..2b23ca2 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
@@ -870,7 +870,7 @@ static void mlx4_en_set_default_moderation(struct mlx4_en_priv *priv)
 	/* If we haven't received a specific coalescing setting
 	 * (module param), we set the moderation parameters as follows:
 	 * - moder_cnt is set to the number of mtu sized packets to
-	 *   satisfy our coelsing target.
+	 *   satisfy our coalescing target.
 	 * - moder_time is set to a fixed value.
 	 */
 	priv->rx_frames = MLX4_EN_RX_COAL_TARGET;
diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
index 9d27e42..8a5e70d 100644
--- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
+++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
@@ -126,7 +126,7 @@ enum {
 #define MLX4_EN_RX_COAL_TIME	0x10
 
 #define MLX4_EN_TX_COAL_PKTS	16
-#define MLX4_EN_TX_COAL_TIME	0x80
+#define MLX4_EN_TX_COAL_TIME	0x10
 
 #define MLX4_EN_RX_RATE_LOW		400000
 #define MLX4_EN_RX_COAL_TIME_LOW	0


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