From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michael Wang Subject: Re: [PATCH] Avoid extra calculation in ip_route_input_common Date: Wed, 21 Dec 2011 13:19:57 +0800 Message-ID: <4EF16C7D.1060608@linux.vnet.ibm.com> References: <4EF16AA3.2070303@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "netdev@vger.kernel.org" To: Michael Wang Return-path: Received: from e28smtp04.in.ibm.com ([122.248.162.4]:59083 "EHLO e28smtp04.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751097Ab1LUFUF (ORCPT ); Wed, 21 Dec 2011 00:20:05 -0500 Received: from /spool/local by e28smtp04.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 21 Dec 2011 10:50:02 +0530 Received: from d28av03.in.ibm.com (d28av03.in.ibm.com [9.184.220.65]) by d28relay05.in.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id pBL5JxdN2404438 for ; Wed, 21 Dec 2011 10:49:59 +0530 Received: from d28av03.in.ibm.com (loopback [127.0.0.1]) by d28av03.in.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id pBL5Jwo6017791 for ; Wed, 21 Dec 2011 16:19:58 +1100 In-Reply-To: <4EF16AA3.2070303@linux.vnet.ibm.com> Sender: netdev-owner@vger.kernel.org List-ID: 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 > > 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 > --- > 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)) {