netdev - Re: [PATCH 3/6] IPV4 : use xor rather than multiple ands for route compare

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Date:	Thu, 10 Apr 2008 01:51:18 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	shemminger@...tta.com
Cc:	dada1@...mosbay.com, netdev@...r.kernel.org
Subject: Re: [PATCH 3/6] IPV4 : use xor rather than multiple ands for route
 compare

From: Stephen Hemminger <shemminger@...tta.com>
Date: Tue, 1 Apr 2008 13:08:42 -0700

> The flow fields are all together, and the other parameters are local variables
> in registers so that compare should be in one cache line.
> 
> --- a/net/ipv4/route.c	2008-03-31 17:12:30.000000000 -0700
> +++ b/net/ipv4/route.c	2008-04-01 13:05:46.000000000 -0700
> @@ -2079,12 +2079,12 @@ int ip_route_input(struct sk_buff *skb, 
>  	rcu_read_lock();
>  	for (rth = rcu_dereference(rt_hash_table[hash].chain); rth;
>  	     rth = rcu_dereference(rth->u.dst.rt_next)) {
> -		if (rth->fl.fl4_dst == daddr &&
> -		    rth->fl.fl4_src == saddr &&
> -		    rth->fl.iif == iif &&
> -		    rth->fl.oif == 0 &&
> +		if (((rth->fl.fl4_dst ^ daddr) |
> +		     (rth->fl.fl4_src ^ saddr) |
> +		     (rth->fl.iif ^ iif) |
> +		     rth->fl.oif |
> +		     (rth->fl.fl4_tos ^ tos)) == 0 &&
>  		    rth->fl.mark == skb->mark &&
> -		    rth->fl.fl4_tos == tos &&
>  		    net_eq(dev_net(rth->u.dst.dev), net) &&
>  		    rth->rt_genid == atomic_read(&rt_genid)) {
>  			dst_use(&rth->u.dst, jiffies);

Eric, any objections to this version?
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