netdev - Re: [PATCH net-next V2] net/vxlan: Avoid unaligned access in vxlan_build

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Message-ID: <20160921161457.GA17116@ast-mbp.thefacebook.com>
Date:   Wed, 21 Sep 2016 09:14:59 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:     Sowmini Varadhan <sowmini.varadhan@...cle.com>,
        netdev@...r.kernel.org, jbenc@...hat.com, davem@...emloft.net
Subject: Re: [PATCH net-next V2] net/vxlan: Avoid unaligned access in
 vxlan_build_skb()

On Wed, Sep 21, 2016 at 12:10:55PM +0200, Hannes Frederic Sowa wrote:
> On 20.09.2016 20:57, Sowmini Varadhan wrote:
> > The vxlan header may not be aligned to 4 bytes in
> > vxlan_build_skb (e.g., for MLD packets). This patch
> > avoids unaligned access traps from vxlan_build_skb
> > (in platforms like sparc) by making struct vxlanhdr __packed.
> > 
> > Signed-off-by: Sowmini Varadhan <sowmini.varadhan@...cle.com>
> 
> Performance wise this should only affect code generation for archs where
> it matters anyway.

I think it's the opposite. Even on x86 compiler will use byte loads.