netdev - Re: [PATCH net] gso: Update tunnel segmentation to support Tx checksum offload

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Date:	Wed, 10 Jul 2013 14:21:46 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexander Duyck <alexander.h.duyck@...el.com>
Cc:	netdev@...r.kernel.org, stephen@...workplumber.org,
	pshelar@...ira.com, joseph.gasparakis@...el.com
Subject: Re: [PATCH net] gso: Update tunnel segmentation to support Tx
 checksum offload

On Wed, 2013-07-10 at 13:43 -0700, Alexander Duyck wrote:
> This change makes it so that the GRE and VXLAN tunnels can make use of Tx
> checksum offload support provided by some drivers via the hw_enc_features.
> This resolves a performance regression seen when using TSO versus just
> using the Tx checksum offload.
> 
> To achieve this it was necessary to address two items.  First
> netif_skb_features needed to be updated so that it would correctly handle
> the Trans Ether Bridging protocol.  To that end the reference to
> skb->protocol was replaced with a call to skb_network_protocol.
> 
> Second it was necessary to update the GRE and UDP tunnel segmentation
> offloads so that they would reset the encapsulation bit and inner header
> offsets after the offload was complete.
> 
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...el.com>
> ---
> 
> I am submitting this as a fix for 3.11 and stable, however the fix for
> stable would likely need some modification since it seems that gre.c was
> renamed to gre_offload.c at some point between 3.10 and 3.11.  If needed
> I can submit a separate patch for stable.
> 
>  net/core/dev.c         |    2 +-
>  net/ipv4/gre_offload.c |    3 +++
>  net/ipv4/udp.c         |    4 +++-
>  3 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 560dafd..0419961 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -2495,7 +2495,7 @@ static netdev_features_t harmonize_features(struct sk_buff *skb,
>  
>  netdev_features_t netif_skb_features(struct sk_buff *skb)
>  {
> -	__be16 protocol = skb->protocol;
> +	__be16 protocol = skb_network_protocol(skb);
>  	netdev_features_t features = skb->dev->features;
>  

If we call skb_network_protocol() here, do we still need following tests
in netif_skb_features() ?

if (protocol == htons(ETH_P_8021Q) || protocol == htons(ETH_P_8021AD)) {
 ...
} else if (!vlan_tx_tag_present(skb)) {
}



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