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

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Date:	Fri, 11 Jul 2014 08:57:12 -0700
From:	Jerry Chu <hkchu@...gle.com>
To:	Wolfgang Walter <linux@...m.de>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>
Subject: Re: GRO: very bad routing performance with 3.14.4 for GRE-packets

On Thu, Jul 10, 2014 at 7:34 AM, Wolfgang Walter <linux@...m.de> wrote:
> Am Dienstag, 8. Juli 2014, 17:19:33 schrieb Jerry Chu:
>> 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.
>
> Yes, this patch fixes the problem.
>
> Is there any chance this will make it into 3.14, soon?

Will try to resubmit the patch soon.

>
> I would recommend to revert bf5a755f5e9186406bbf50f4087100af5bd68e40 in 3.14
> for now and reapply it when this fix is available as this is a real
> regression.
>
> Thanks for your help.
>
> Regards,
> --
> Wolfgang Walter
> Studentenwerk München
> Anstalt des öffentlichen Rechts
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