Subject: Re: [PATCH] Avoid extra calculation in ip_route_input_common

From: Michael Wang <[email-masked]>
Date: Wed, 21 Dec 2011 13:19:57 +0800

Please tell me if this patch is silly...
I really want to know the reason we need to use ^ and | instead of if and &&.

On 12/21/2011 01:12 PM, Michael Wang wrote:

> From: Michael Wang <[email-masked]>
> 
> If previous condition doesn't meet, the later check will be cancelled.
> So we don't need to do all the calculation.
> 
> Signed-off-by: Michael Wang <[email-masked]>
> ---
>  net/ipv4/route.c |    8 ++++----
>  1 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv4/route.c b/net/ipv4/route.c
> index f30112f..2872bfb 100644
> --- a/net/ipv4/route.c
> +++ b/net/ipv4/route.c
> @@ -2362,10 +2362,10 @@ int ip_route_input_common(struct sk_buff *skb, __be32 daddr, __be32 saddr,
> 
>  	for (rth = rcu_dereference(rt_hash_table[hash].chain); rth;
>  	     rth = rcu_dereference(rth->dst.rt_next)) {
> -		if ((((__force u32)rth->rt_key_dst ^ (__force u32)daddr) |

And I also wonder whether I can use "rth->rt_key_dst == daddr" here or not...

Thanks & Regards,
Michael Wang

> -		     ((__force u32)rth->rt_key_src ^ (__force u32)saddr) |
> -		     (rth->rt_route_iif ^ iif) |
> -		     (rth->rt_key_tos ^ tos)) == 0 &&
> +		if (((__force u32)rth->rt_key_dst ^ (__force u32)daddr) == 0 &&
> +		    ((__force u32)rth->rt_key_src ^ (__force u32)saddr) == 0 &&
> +		    rth->rt_route_iif == iif &&
> +		    rth->rt_key_tos == tos &&
>  		    rth->rt_mark == skb->mark &&
>  		    net_eq(dev_net(rth->dst.dev), net) &&
>  		    !rt_is_expired(rth)) {