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Date: Fri, 27 Dec 2013 21:12:37 +0100 (CET)
From: Julia Lawall <julia.lawall@lip6.fr>
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To: Joe Perches <joe@perches.com>
cc: Eric Dumazet <eric.dumazet@gmail.com>, Julia Lawall <julia.lawall@lip6.fr>,
        Ding Tianhong <dingtianhong@huawei.com>,
        "David S. Miller" <davem@davemloft.net>,
        Netdev <netdev@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net-next 19/20] net: plip: slight optimization of addr
 compare
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On Fri, 27 Dec 2013, Joe Perches wrote:

> On Fri, 2013-12-27 at 07:48 -0800, Eric Dumazet wrote:
> > On Fri, 2013-12-27 at 14:49 +0800, Ding Tianhong wrote:
> > > Use possibly more efficient ether_addr_equal
> > > to instead of memcmp.
> []
> > > diff --git a/drivers/net/plip/plip.c b/drivers/net/plip/plip.c
> []
> > > @@ -549,7 +549,7 @@ static __be16 plip_type_trans(struct sk_buff *skb, struct net_device *dev)
> > >  
> > >  	if(*eth->h_dest&1)
> > >  	{
> > > -		if(memcmp(eth->h_dest,dev->broadcast, ETH_ALEN)==0)
> > > +		if(ether_addr_equal(eth->h_dest, dev->broadcast))
> > >  			skb->pkt_type=PACKET_BROADCAST;
> > >  		else
> > >  			skb->pkt_type=PACKET_MULTICAST;
> > 
> > What about :
> > 
> >         if (is_multicast_ether_addr(eth->h_dest)) {
> >                 if (ether_addr_equal_64bits(eth->h_dest, dev->broadcast))
> >                         skb->pkt_type = PACKET_BROADCAST;
> >                 else
> >                         skb->pkt_type = PACKET_MULTICAST;
> >         }
> 
> That is better though I wonder how many systems are
> still using laplink via parallel null-printer cables.
> 
> No matter, better is better.
> 
> The same optimization using ether_addr_equal_64bits
> may be possible to do in other places given other
> structs too.
> 
> Perhaps it's a possible spatch/coccinelle conversion,
> 
> I don't know spatch well enough to know if a
> mechanism to check if structure members have other
> fields that follow them in the structure or if the
> structure member is an array of a minimum size.
> 
> Maybe Julia does.  (cc'd)

I'm not sure to competely understand the issues.  Could you explain more?

thanks,
julia