From mboxrd@z Thu Jan 1 00:00:00 1970 From: ebiederm@xmission.com (Eric W. Biederman) Subject: Re: [PATCH 1/2] net: Allow to create links with given ifindex Date: Thu, 02 Aug 2012 04:09:39 -0700 Message-ID: <87wr1h35zg.fsf@xmission.com> References: <50160EEF.6050406@parallels.com> <87pq7dh6b2.fsf@xmission.com> <87fw89h5zk.fsf@xmission.com> <50179F66.1000604@parallels.com> <878ve0dtw3.fsf@xmission.com> <1343903310.9299.184.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain Cc: Pavel Emelyanov , Linux Netdev List , David Miller To: Eric Dumazet Return-path: Received: from out01.mta.xmission.com ([166.70.13.231]:34743 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750799Ab2HBLKI (ORCPT ); Thu, 2 Aug 2012 07:10:08 -0400 In-Reply-To: <1343903310.9299.184.camel@edumazet-glaptop> (Eric Dumazet's message of "Thu, 02 Aug 2012 12:28:30 +0200") Sender: netdev-owner@vger.kernel.org List-ID: Eric Dumazet writes: > On Tue, 2012-07-31 at 04:58 -0700, Eric W. Biederman wrote: > >> Making lo the particularly interesting case. > > > BTW, I noticed in my benchmarks, that once I remove the contention on > dst refcnt (using a percpu cache of dsts), I have a strange performance > cost accessing net->loopback_dev->ifindex in ip_route_output_key. > > Strange because I see no false sharing on this ifindex location for > loopback device. > > So we probably can save some cycles adding a net->loopback_ifindex > to remove one dereference. I am going to let Pavel tackle the actual work because only migration really cares and he is working on migration right now. But assuming we merge the per network namespace ifindex counter we can change net->loopback_dev->ifindex to LOOPBACK_IFINDEX and define "#define LOOPBACK_IFINDEX 1" Certainly that works in the initial network namespace today and might be worth testing. > If ifindex are per network space, I guess we'll need to change > arp_hashfn() or else we'll use some slots more than others. Darn. I hate being right about there being a few places to fix up. ndisc_hashfn also has the same limitation. Eric > diff --git a/include/net/arp.h b/include/net/arp.h > index 7f7df93..37aac58 100644 > --- a/include/net/arp.h > +++ b/include/net/arp.h > @@ -10,7 +10,7 @@ extern struct neigh_table arp_tbl; > > static inline u32 arp_hashfn(u32 key, const struct net_device *dev, u32 hash_rnd) > { > - u32 val = key ^ dev->ifindex; > + u32 val = key ^ (u32)(unsigned long)dev; > > return val * hash_rnd; > }