From: Joe Perches <joe@perches.com>
To: Michael Wang <wangyun@linux.vnet.ibm.com>,
Stephen Hemminger <shemminger@vyatta.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: Re: [PATCH] Avoid extra calculation in ip_route_input_common
Date: Tue, 20 Dec 2011 21:23:53 -0800 [thread overview]
Message-ID: <1324445033.20505.2.camel@joe2Laptop> (raw)
In-Reply-To: <4EF16AA3.2070303@linux.vnet.ibm.com>
On Wed, 2011-12-21 at 13:12 +0800, Michael Wang wrote:
> From: Michael Wang <wangyun@linux.vnet.ibm.com>
>
> If previous condition doesn't meet, the later check will be cancelled.
> So we don't need to do all the calculation.
Not sure about that.
> Signed-off-by: Michael Wang <wangyun@linux.vnet.ibm.com>
> ---
> 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) |
> - ((__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)) {
See:
commit c0b8c32b1c96afc9b32b717927330025cc1c501e
Author: Stephen Hemminger <shemminger@vyatta.com>
Date: Thu Apr 10 04:00:28 2008 -0700
IPV4: use xor rather than multiple ands for route compare
The comparison in ip_route_input is a hot path, by recoding the C
"and" as bit operations, fewer conditional branches get generated
so the code should be faster. Maybe someday Gcc will be smart
enough to do this?
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
next prev parent reply other threads:[~2011-12-21 5:23 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-21 5:12 [PATCH] Avoid extra calculation in ip_route_input_common Michael Wang
2011-12-21 5:19 ` Michael Wang
2011-12-21 5:23 ` Joe Perches [this message]
2011-12-21 5:39 ` Michael Wang
2011-12-21 5:50 ` Joe Perches
2011-12-21 6:00 ` Michael Wang
2011-12-21 5:57 ` David Miller
2011-12-21 6:04 ` Michael Wang
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