netdev - Re: GRO: very bad routing performance with 3.14.4 for GRE-packets

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Date:	Tue, 8 Jul 2014 17:19:33 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Wolfgang Walter <linux@...m.de>, netdev <netdev@...r.kernel.org>
Subject: Re: GRO: very bad routing performance with 3.14.4 for GRE-packets

On Tue, Jul 8, 2014 at 3:44 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Tue, 2014-07-08 at 22:35 +0200, Wolfgang Walter wrote:
>> Hello,
>>
>> I upgraded a router from 3.10.46 to 3.14.4 and I see a dramatic perfomance
>> loss for GRE-pakets if (and only if) GRO is enabled on the incoming or
>> outgoing interface (drops to 1/50th to 1/100th).
>>
>> Other traffic is just fine.
>>
>> The router itself is not endpoint of the GRE-tunnel.
>>
>> The router has connection tracking enabled and does NAT (but most of the
>> traffic is not NATed nor are GRE-packets).
>>
>> The network card is an Intel Corporation I350 Gigabit (both interfaces).
>>
>> Regards,
>
> GRO is a win if the consumer of the packets understands GSO packets.
>
> In this case, Intel driver is not able to send GSO packets with GRE
> encapsulation, so they need to be segmented before being sent.
>
> That's extra work and not worth it, as you noticed.
>
> One way to get good performance would be to implement a software TSO in
> the Intel driver for the GRE encapsulated packets.
>
> You might revert bf5a755f5e9186406bbf50f4087100af5bd68e40, or submit a
> patch to make the GRE handling in GRO an optional feature.
>

There is also a bug to the forwarding path introduced by my GRE-GRO
patch that I discovered a while back and submitted a fix to it. Please
see http://patchwork.ozlabs.org/patch/324953/ and let me know if that
addresses the problem you've seen. Sorry I have not got the time to
follow through with the patch.
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