netdev - Re: [PATCH net-next] net: ipv6/gre: Add GRO support

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Date:   Mon, 2 Apr 2018 18:45:41 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Eran Ben Elisha <eranlinuxmellanox@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next] net: ipv6/gre: Add GRO support



On 02/04/2018 6:19 PM, Eric Dumazet wrote:
> 
> 
> On 04/02/2018 08:00 AM, Eran Ben Elisha wrote:
>>>>> Seems good, but why isn't this handled directly in GRO native layer ?
>>>> ip6_tunnel and ip6_gre do not share initialization flow functions (unlike ipv4).
>>>> Changing the ipv6 init infrastructure should not be part of this
>>>> patch. we prefer to keep this one minimal, simple and safe.
>>>
>>>
>>>
>>> Looking at gre_gro_receive() and gre_gro_complete() I could not see why they
>>> could not be copied/pasted to IPv6.
>>
>> These functions to handle GRO over GRE are already assigned in
>> gre_offload_init() (in net/ipv4/gre_offload.c under CONFIG_IPV6).
>> However without initializing the gro_cells, the receive path will not
>> go via napi_gro_receive path, but directly to netif_rx.
>> So AFAIU, only gcells->cells was missing for gro_cells_receive to
>> really go via GRO flow.
>>
>>>
>>> Maybe give more details on the changelog, it is really not obvious.
>> Hopefully the above filled this request.
>>>
> 
> Not really :/
> 

So you're referring to native interface. We thought you meant native IP 
module.


> gro_cells_receive() is not really useful with native GRO, since packet is already
> a GRO packet by the time it reaches ip_tunnel_rcv() or __ip6_tnl_rcv()
> 

Right. If GRO on native interface is ON, our patch doesn't help much.
The case we improve here is:
Native has GRO OFF, GRE has GRO ON.

Before this patch there were no GRO packets at all in this case, only 
MTU packets went up the stack.

> Sure, it might be usefull if native GRO (happening on eth0 if you prefer) did not
> handle a particular encapsulation.
> 

Or it is turned OFF.

> gro_cell was a work around before we extended GRO to be able to decap some tunnel headers.
> 
> It seems we have to extend this to also support GRE6.
>