netdev - Re: [PATCH net-next V2 0/2] Mellanox 100G mlx5 minimum inline header mode

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Date:	Tue, 26 Jul 2016 14:29:47 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	hadarh@....mellanox.co.il
Cc:	saeedm@...lanox.com, netdev@...r.kernel.org, ogerlitz@...lanox.com,
	hadarh@...lanox.com
Subject: Re: [PATCH net-next V2 0/2] Mellanox 100G mlx5 minimum inline
 header mode

From: Hadar Hen Zion <hadarh@....mellanox.co.il>
Date: Tue, 26 Jul 2016 13:30:46 +0300

> In the default case eth_get_headlen() won't be called, it will happen
> only if PF administrator changes the mode from default to L4.
> 
> In L4 mode, we need to copy all the packet headers including L4, do
> you know of a better/cheaper way for doing that?

You can just look straight at the ethernet header in this context.

eth_get_headlen() is expensive and has a complete header parser.  It
is meant to be used when none of the SKB context state has been setup
yet (early RX processing before SKB is allocated, for example).