From: Xin Long <lucien....@gmail.com> Date: Mon, 18 Dec 2017 14:20:56 +0800
> 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. > > Note that this patch doesn't process any pmtu icmp packet. > But even in the future, the support for pmtu icmp packets > process of udp tunnels will also needs this. > > The same thing will be done for geneve in another patch. > > Signed-off-by: Xin Long <lucien....@gmail.com> Yikes... You're going to have to find a way to fix this without invoking ->update_pmtu() on every single transmit. That's really excessive, especially for an operation which is going to be a NOP %99.9999 of the time. We need some way, instead, for the MTU change event to propagate properly. I know this might be hard, but doing this in the transmit handler on every packet to deal with it is not the way to go. Thanks.
