linux-kernel - Re: [PATCH net-next 19/20] net: plip: slight optimization of addr compare

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Date:	Fri, 27 Dec 2013 09:06:22 -0800
From:	Joe Perches <joe@...ches.com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Julia Lawall <julia.lawall@...6.fr>
Cc:	Ding Tianhong <dingtianhong@...wei.com>,
	"David S. Miller" <davem@...emloft.net>,
	Netdev <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next 19/20] net: plip: slight optimization of addr
 compare

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)

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