netdev - Re: GRO aggregation

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Date:	Thu, 13 Sep 2012 14:34:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Or Gerlitz <or.gerlitz@...il.com>
Cc:	Shlomo Pongartz <shlomop@...lanox.com>,
	Rick Jones <rick.jones2@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Tom Herbert <therbert@...gle.com>
Subject: Re: GRO aggregation

On Thu, 2012-09-13 at 14:05 +0200, Eric Dumazet wrote:

> But there is no real difference in throughput.
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> index 6c4f935..435c35e 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> +++ b/drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
> @@ -96,8 +96,8 @@
>  /* Receive fragment sizes; we use at most 4 fragments (for 9600 byte MTU
>   * and 4K allocations) */
>  enum {
> -	FRAG_SZ0 = 512 - NET_IP_ALIGN,
> -	FRAG_SZ1 = 1024,
> +	FRAG_SZ0 = 1536 - NET_IP_ALIGN,
> +	FRAG_SZ1 = 2048,
>         FRAG_SZ2 = 4096,
>         FRAG_SZ3 = MLX4_EN_ALLOC_SIZE
>  };
> 

Oh well, adding one prefetch() is giving ~10% more throughput.

I guess this mlx4 driver needs some care.

diff --git a/drivers/net/ethernet/mellanox/mlx4/en_rx.c b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
index 5aba5ec..547eec8 100644
--- a/drivers/net/ethernet/mellanox/mlx4/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx4/en_rx.c
@@ -38,6 +38,7 @@
 #include <linux/if_ether.h>
 #include <linux/if_vlan.h>
 #include <linux/vmalloc.h>
+#include <linux/prefetch.h>
 
 #include "mlx4_en.h"
 
@@ -617,7 +618,8 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
 		    !((dev->features & NETIF_F_LOOPBACK) ||
 		      priv->validate_loopback))
 			goto next;
-
+		/* avoid cache miss in tcp_gro_receive() */
+		prefetch((char *)ethh + 64);
 		/*
 		 * Packet is OK - process it.
 		 */


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