netdev - Re: [PATCH net-next] gro: Handle inline VLAN tags

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Date:	Fri, 16 Nov 2012 20:17:24 -0500
From:	Andrew Gallatin <gallatin@...i.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-net-drivers@...arflare.com,
	Eric Dumazet <eric.dumazet@...il.com>,
	Herbert Xu <herbert@...dor.hengli.com.au>
Subject: Re: [PATCH net-next] gro: Handle inline VLAN tags

On 11/16/12 15:17, Ben Hutchings wrote:
> The receive paths for skbs with inline and out-of-line VLAN tags (VLAN
> RX accleration) were made largely consistent in 2.6.37, with tags
> pulled out by software as necessary.  However GRO doesn't do this, so
> it is not effective for VLAN-tagged packets received on devices
> without VLAN RX acceleration.
>
> napi_gro_frags() must not free the skb and does not advance the
> skb->data pointer, so cannot use vlan_untag().  Extract the core of
> vlan_untag() into a new function __vlan_untag() that allows the offset
> to the VLAN tag to be specified and returns an error code.  Add
> kernel-doc comments for both those functions.
>
> Signed-off-by: Ben Hutchings <bhutchings@...arflare.com>
> ---
> Tested with sfc using both napi_gro_receive() and napi_gro_frags().  On
> a Core i7 920 (Nehalem) system it increased TCP/IPv4 receive throughput
> over a VLAN from ~8.0 to ~9.3 Gbit/s.


I verified similar results on myri10ge, using my recent GRO
patchset (minus the in-driver vtag removal) with just
napi_gro_frags().

I've no strong feeling as to whether or not this belongs in GRO or the
driver.  I'm just glad that it is being discussed.

Thank you,

Drew

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