From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754794Ab3L0UrF (ORCPT ); Fri, 27 Dec 2013 15:47:05 -0500 Received: from smtprelay0024.hostedemail.com ([216.40.44.24]:45436 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1754725Ab3L0UrD (ORCPT ); Fri, 27 Dec 2013 15:47:03 -0500 X-Session-Marker: 6A6F6540706572636865732E636F6D X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,joe@perches.com,:::::::::::,RULES_HIT:41:355:379:541:599:973:988:989:1260:1261:1277:1311:1313:1314:1345:1359:1373:1437:1515:1516:1518:1534:1542:1593:1594:1711:1730:1747:1777:1792:1801:2393:2553:2559:2562:2692:2828:2901:3138:3139:3140:3141:3142:3355:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4321:4605:5007:7652:8603:10004:10400:10450:10455:10481:10848:11026:11232:11658:11914:12043:12296:12438:12517:12519:12663:12740:13071:13161:13229:19900:19904:19999:21060,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: lace31_201650cc6503b X-Filterd-Recvd-Size: 3712 Message-ID: <1388177217.30298.24.camel@joe-AO722> Subject: Re: [PATCH net-next 19/20] net: plip: slight optimization of addr compare From: Joe Perches To: Julia Lawall Cc: Eric Dumazet , Ding Tianhong , "David S. Miller" , Netdev , "linux-kernel@vger.kernel.org" Date: Fri, 27 Dec 2013 12:46:57 -0800 In-Reply-To: References: <52BD22ED.4030302@huawei.com> <1388159283.12212.80.camel@edumazet-glaptop2.roam.corp.google.com> <1388163982.30298.12.camel@joe-AO722> Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: Evolution 3.8.4-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2013-12-27 at 21:12 +0100, Julia Lawall wrote: > 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? Hi Julia. Maybe this explanation is helpful? ethernet addresses are u8[6] (48 bits) ether_addr_equal_64bits gets passed a pointer to u8[8] and is more efficient on 64 bit architectures than ether_addr_equal because the test can be done with a single compare and shift. The idea is not to access past the end of the ethernet address as appropriate (think pointer to eeprom or other such end-of-addressable memory conditions) If a struct containing an ethernet address has additional members after the ethernet address, or the u8[6] address passed to ether_addr_equal is not going to access past the end of memory or the structure, then ether_addr_equal_64bits should be used in lieu of ether_addr_equal. Joe