netdev - Re: [RFC PATCH 2/5] mlx5: Add support for UDP tunnel segmentation with outer checksum offload

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Date:	Thu, 28 Apr 2016 21:43:04 +0000
From:	Matthew Finlay <Matt@...lanox.com>
To:	Alexander Duyck <alexander.duyck@...il.com>,
	Saeed Mahameed <saeedm@....mellanox.co.il>
CC:	Alexander Duyck <aduyck@...antis.com>,
	Eugenia Emantayev <eugenia@...lanox.com>,
	Bruce W Allan <bruce.w.allan@...el.com>,
	"Saeed Mahameed" <saeedm@...lanox.com>,
	Linux Netdev List <netdev@...r.kernel.org>,
	intel-wired-lan <intel-wired-lan@...ts.osuosl.org>,
	Ariel Elior <ariel.elior@...gic.com>,
	Michael Chan <mchan@...adcom.com>
Subject: Re: [RFC PATCH 2/5] mlx5: Add support for UDP tunnel segmentation
 with outer checksum offload






On 4/20/16, 11:06 AM, "Alexander Duyck" <alexander.duyck@...il.com> wrote:

>On Wed, Apr 20, 2016 at 10:40 AM, Saeed Mahameed
><saeedm@....mellanox.co.il> wrote:
>> On Tue, Apr 19, 2016 at 10:06 PM, Alexander Duyck <aduyck@...antis.com> wrote:
>>> This patch assumes that the mlx5 hardware will ignore existing IPv4/v6
>>> header fields for length and checksum as well as the length and checksum
>>> fields for outer UDP headers.
>>>
>>> I have no means of testing this as I do not have any mlx5 hardware but
>>> thought I would submit it as an RFC to see if anyone out there wants to
>>> test this and see if this does in fact enable this functionality allowing
>>> us to to segment UDP tunneled frames that have an outer checksum.
>>>
>>> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
>>> ---
>>>  drivers/net/ethernet/mellanox/mlx5/core/en_main.c |    7 ++++++-
>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>> index e0adb604f461..57d8da796d50 100644
>>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>>> @@ -2390,13 +2390,18 @@ static void mlx5e_build_netdev(struct net_device *netdev)
>>>         netdev->hw_features      |= NETIF_F_HW_VLAN_CTAG_FILTER;
>>>
>>>         if (mlx5e_vxlan_allowed(mdev)) {
>>> -               netdev->hw_features     |= NETIF_F_GSO_UDP_TUNNEL;
>>> +               netdev->hw_features     |= NETIF_F_GSO_UDP_TUNNEL |
>>> +                                          NETIF_F_GSO_UDP_TUNNEL_CSUM |
>>> +                                          NETIF_F_GSO_PARTIAL;
>>>                 netdev->hw_enc_features |= NETIF_F_IP_CSUM;
>>>                 netdev->hw_enc_features |= NETIF_F_RXCSUM;
>>>                 netdev->hw_enc_features |= NETIF_F_TSO;
>>>                 netdev->hw_enc_features |= NETIF_F_TSO6;
>>>                 netdev->hw_enc_features |= NETIF_F_RXHASH;
>>>                 netdev->hw_enc_features |= NETIF_F_GSO_UDP_TUNNEL;
>>> +               netdev->hw_enc_features |= NETIF_F_GSO_UDP_TUNNEL_CSUM |
>>> +                                          NETIF_F_GSO_PARTIAL;
>>> +               netdev->gso_partial_features = NETIF_F_GSO_UDP_TUNNEL_CSUM;
>>>         }
>>>
>>>         netdev->features          = netdev->hw_features;
>>>
>>
>> Hi Alex,
>>
>> Adding Matt, VxLAN feature owner from Mellanox,
>> Matt please correct me if am wrong, but We already tested GSO VxLAN
>> and we saw the TCP/IP checksum offloads for both inner and outer
>> headers handled by the hardware.
>>
>> And looking at mlx5e_sq_xmit:
>>
>> if (likely(skb->ip_summed == CHECKSUM_PARTIAL)) {
>>         eseg->cs_flags = MLX5_ETH_WQE_L3_CSUM;
>> if (skb->encapsulation) {
>>         eseg->cs_flags |= MLX5_ETH_WQE_L3_INNER_CSUM |
>> MLX5_ETH_WQE_L4_INNER_CSUM;
>>         sq->stats.csum_offload_inner++;
>> } else {
>>         eseg->cs_flags |= MLX5_ETH_WQE_L4_CSUM;
>> }
>>
>> We enable inner/outer hardware checksumming unconditionally without
>> looking at the features Alex is suggesting in this patch,
>> Alex, can you elaborate more on the meaning of those features ? and
>> why would it work for us without declaring them ?
>
>Well right now the feature list exposed by the device indicates that
>TSO is not used if a VxLAN tunnel has a checksum in an outer header.
>Since that is not exposed currently that is completely offloaded in
>software via GSO.

The mlx5 hardware requires the outer UDP checksum is not set when offloading encapsulated packets. 

>
>What the GSO partial does is allow us to treat GSO for tunnels with
>checksum like it is GSO for tunnels without checksum by precomputing
>the UDP checksum as though the frame had already been segmented and
>restricts us to an even multiple of MSS bytes that are to be segmented
>between all the frames.  One side effect though is that all of the IP
>and UDP header fields are also precomputed, but from what I can tell
>it looks like the values that would be changed by a change in length
>are ignored or overwritten by the hardware and driver anyway.
>
>- Alex