Re: Large performance regression with 6in4 tunnel (sit)

From: "Stephen Rothwell" <redacted>
To: "Sven-Haegar Koch" <redacted>
Cc: "Eli Cooper" <redacted>, netdev@vger.kernel.org, "Eric Dumazet" <redacted>
Sent: Saturday, November 26, 2016 10:23:40 PM
Subject: Re: Large performance regression with 6in4 tunnel (sit)

Hi Sven-Haegar,

On Fri, 25 Nov 2016 05:06:53 +0100 (CET) Sven-Haegar Koch [off-list ref]
wrote:

quoted

Somehow this problem description really reminds me of a report on
netdev a bit ago, which the following patch fixed:

commit 9ee6c5dc816aa8256257f2cd4008a9291ec7e985
Author: Lance Richardson [off-list ref]
Date:   Wed Nov 2 16:36:17 2016 -0400

    ipv4: allow local fragmentation in ip_finish_output_gso()
    
    Some configurations (e.g. geneve interface with default
    MTU of 1500 over an ethernet interface with 1500 MTU) result
    in the transmission of packets that exceed the configured MTU.
    While this should be considered to be a "bad" configuration,
    it is still allowed and should not result in the sending
    of packets that exceed the configured MTU.

Could this be related?

I suppose it would be difficult to test this patch on this machine?

The kernel I am running on is based on 4.7.8, so the above patch
doesn't come close to applying. Most fo what it is reverting was
introduced in commit 359ebda25aa0 ("net/ipv4: Introduce IPSKB_FRAG_SEGS
bit to inet_skb_parm.flags") in v4.8-rc1.

--
Cheers,
Stephen Rothwell

This should be equivalent for 4.7.x:

diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 4bd4921..8a253e2 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c

@@ -224,8 +224,7 @@ static int ip_finish_output_gso(struct net *net, struct sock *sk,
        int ret = 0;
 
        /* common case: locally created skb or seglen is <= mtu */
-       if (((IPCB(skb)->flags & IPSKB_FORWARDED) == 0) ||
-             skb_gso_network_seglen(skb) <= mtu)
+       if (skb_gso_network_seglen(skb) <= mtu)
                return ip_finish_output2(net, sk, skb);
 
        /* Slowpath -  GSO segment length is exceeding the dst MTU.