netdev - Re: [PATCH net] vxlan: update skb dst pmtu on tx path

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Message-ID: <CADvbK_f8_Sd-pM91KGYiLBNhLfwp9nztULSwa90yHQXOOpobEQ@mail.gmail.com>
Date:   Tue, 23 Jan 2018 17:00:13 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     Roman Kapl <code@...pl.cz>
Cc:     network dev <netdev@...r.kernel.org>, davem <davem@...emloft.net>,
        Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH net] vxlan: update skb dst pmtu on tx path

On Tue, Jan 23, 2018 at 6:35 AM, Roman Kapl <code@...pl.cz> wrote:
> On 12/18/2017 07:20 AM, Xin Long wrote:
>>
>> Unlike ip tunnels, now vxlan doesn't do any pmtu update for
>> upper dst pmtu, even if it doesn't match the lower dst pmtu
>> any more.
>>
>> The problem can be reproduced when reducing the vxlan lower
>> dev's pmtu when running netperf. In jianlin's testing, the
>> performance went to 1/7 of the previous.
>>
>> This patch is to update the upper dst pmtu to match the lower
>> dst pmtu on tx path so that packets can be sent out even when
>> lower dev's pmtu has been changed.
>>
>> It also works for metadata dst.
>
> Sorry for resurrecting the conversation, but what exactly was meant by this
> "works metadata dst" remark? I am currently having kernel crashes related to
> ops->update_pmtu == NULL on VXLAN xmit and I am using tunnel metadata set by
> act_tunnel_key. Before this patch, it was OK.
You are right, it is introudced by this patch.

Jiri Benc mentioned about this patch on md_dst, then I wrote a test
case with ip route
running over it. It worked well, now I realized I cleaned up the env too fast.

Pls also fix it on geneve_xmit. thanks.

>
> My first thought was to add `if (ops->update_pmtu != NULL)`, but it appears
> some thought was given to this. Or maybe md_dst_ops should have update pmtu?
md_dst_ops doesn't support pmtu, I had no plans for it yet by now.

>
> Thanks, Roman Kapl