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

Julia Lawall
2013-12-27T20:12:37Z

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