netdev - Re: [PATCH net-next] gso: enable udp gso for virtual devices

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Message-ID: <d5dea281-67c0-1385-95c1-b476825e6afa@akamai.com>
Date:   Wed, 26 Jun 2019 15:15:05 -0400
From:   Jason Baron <jbaron@...mai.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, Joshua Hunt <johunt@...mai.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next] gso: enable udp gso for virtual devices



On 6/14/19 4:53 PM, Jason Baron wrote:
> 
> 
> On 6/13/19 5:20 PM, Willem de Bruijn wrote:
>>>>> @@ -237,6 +237,7 @@ static inline int find_next_netdev_feature(u64 feature, unsigned long start)
>>>>>                                  NETIF_F_GSO_GRE_CSUM |                 \
>>>>>                                  NETIF_F_GSO_IPXIP4 |                   \
>>>>>                                  NETIF_F_GSO_IPXIP6 |                   \
>>>>> +                                NETIF_F_GSO_UDP_L4 |                   \
>>>>>                                  NETIF_F_GSO_UDP_TUNNEL |               \
>>>>>                                  NETIF_F_GSO_UDP_TUNNEL_CSUM)
>>>>
>>>> Are you adding this to NETIF_F_GSO_ENCAP_ALL? Wouldn't it make more
>>>> sense to add it to NETIF_F_GSO_SOFTWARE?
>>>>
>>>
>>> Yes, I'm adding to NETIF_F_GSO_ENCAP_ALL (not very clear from the
>>> context). I will fix the commit log.
>>>
>>> In: 83aa025 udp: add gso support to virtual devices, the support was
>>> also added to NETIF_F_GSO_ENCAP_ALL (although subsequently reverted due
>>> to UDP GRO not being in place), so I wonder what the reason was for that?
>>
>> That was probably just a bad choice on my part.
>>
>> It worked in practice, but if NETIF_F_GSO_SOFTWARE works the same
>> without unexpected side effects, then I agree that it is the better choice.
>>
>> That choice does appear to change behavior when sending over tunnel
>> devices. Might it send tunneled GSO packets over loopback?
>>
>>
> 
> I set up a test case using fou tunneling through a bridge device using
> the udpgso_bench_tx test where packets are not received correctly if
> NETIF_F_GSO_UDP_L4 is added to NETIF_F_GSO_SOFTWARE. If I have it added
> to NETIF_F_GSO_ENCAP_ALL, it does work correctly. So there are more
> fixes required to include it in NETIF_F_GSO_SOFTWARE.
> 
> The use-case I have only requires it to be in NETIF_F_GSO_ENCAP_ALL, but
> if it needs to go in NETIF_F_GSO_SOFTWARE, I can look at what's required
> more next week.
> 

Hi,

I haven't had a chance to investigate what goes wrong with including
NETIF_F_GSO_UDP_L4 in NETIF_F_GSO_SOFTWARE - but I was just wondering if
people are ok with NETIF_F_GSO_UDP_L4 being added to
NETIF_F_GSO_ENCAP_ALL and not NETIF_F_GSO_SOFTWARE (ie the original
patch as posted)?

As I mentioned that is sufficient for my use-case, and its how Willem
originally proposed this.

Thanks,

-Jason



> Thanks,
> 
> -Jason
> 
>>
>>> I agree that NETIF_F_GSO_SOFTWARE seems conceptually more logical and
>>> further I think it adds support for more 'virtual' devices. For example,
>>> I tested loopback with NETIF_F_GSO_UDP_L4 being added to
>>> NETIF_F_GSO_SOFTWARE and it shows a nice performance gain, whereas
>>> NETIF_F_GSO_ENCAP_ALL isn't included for loopback.
>>>
>>> Thanks,
>>>
>>> -Jason