netdev - Re: [PATCH 3/7] mlx4_en: Incoming traffic alignment optimizations

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Date:	Tue, 18 Oct 2011 03:53:19 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Cc:	davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH 3/7] mlx4_en: Incoming traffic alignment optimizations

Le lundi 17 octobre 2011 à 22:17 +0200, Yevgeny Petrilin a écrit :
> Packet headers are copied to skb linear part (which is IP aligned), so there is no reason for
> the scatter entry to be IP aligned.
> 
> Signed-off-by: Yevgeny Petrilin <yevgenyp@...lanox.co.il>
> ---

> @@ -91,7 +91,7 @@
>  /* Receive fragment sizes; we use at most 4 fragments (for 9600 byte MTU
>   * and 4K allocations) */
>  enum {
> -	FRAG_SZ0 = 512 - NET_IP_ALIGN,
> +	FRAG_SZ0 = 2048,
>  	FRAG_SZ1 = 1024,
>  	FRAG_SZ2 = 4096,
>  	FRAG_SZ3 = MLX4_EN_ALLOC_SIZE

Is the 512 -> 2048 change really wanted ? Its not mentioned in changelog
and is confusing.

This means mlx4 lost the ability to use a small frag (512 bytes) to
store small frames.



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