netdev - Re: [PATCH net 1/2] geneve, vxlan: Don't check skb

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Message-ID: <3bb05500-d304-96b1-46cc-af6da2c49bc0@6wind.com>
Date:   Mon, 15 Oct 2018 14:24:24 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     Stefano Brivio <sbrivio@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Xin Long <lucien.xin@...il.com>,
        Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org
Subject: Re: [PATCH net 1/2] geneve, vxlan: Don't check skb_dst() twice

Le 15/10/2018 à 13:08, Stefano Brivio a écrit :
> On Mon, 15 Oct 2018 12:19:41 +0200
> Nicolas Dichtel <nicolas.dichtel@...nd.com> wrote:
> 
>> Le 12/10/2018 à 23:53, Stefano Brivio a écrit :
>>> Commit f15ca723c1eb ("net: don't call update_pmtu unconditionally") avoids
>>> that we try updating PMTU for a non-existent destination, but didn't clean
>>> up cases where the check was already explicit. Drop those redundant checks.  
>> Yes, I leave them to avoid calculating the new mtu value when not needed. We are
>> in the xmit path.
> 
> Before 2/2 of this series, though, we call skb_dst_update_pmtu() (and
> in turn dst->ops->update_pmtu()) for *every* packet with a dst, which
Not if dst is of type md_dst_ops.

> I'd dare saying is by far the most common case. Besides, 2/2 needs
> anyway to calculate the MTU to fix a bug.
> 
> So I think this is a vast improvement overall.
Fair point.