From owner-freebsd-net@FreeBSD.ORG Sun Jun 6 20:56:34 2010 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 687DE10656C5 for ; Sun, 6 Jun 2010 20:56:34 +0000 (UTC) (envelope-from ncrogers@gmail.com) Received: from mail-iw0-f182.google.com (mail-iw0-f182.google.com [209.85.214.182]) by mx1.freebsd.org (Postfix) with ESMTP id 2E6998FC1E for ; Sun, 6 Jun 2010 20:56:33 +0000 (UTC) Received: by iwn5 with SMTP id 5so3386989iwn.13 for ; Sun, 06 Jun 2010 13:56:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:received:date:message-id :subject:from:to:content-type; bh=DqReQuVDfdWwkSHv/6ehCS348HFEtjqG8EXD+EE6F8w=; b=Baz2Z6Nofx0epIiqhWTtdtZ5tYXbOxOPiLBF8uTiojsuDDe4E5Cmj0K3nM3Goz3J20 7e1oZ5UwxSVBmDT+FJ3sqNFZX/Il68FTOR0EqnfcAGz6XywnHdBZuHQV4GKdHLtlXVy/ eaj6l5pkkpbV8H0JkQC0HIVvsQwdSgk+1iet4= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type; b=prSfG4NY8NrMz2lPKVi5gDh11quROgeUjOyIUPW9xNeBi8C+UAwG65n9L4e83cS7Xk bK03EeQr3aVf4lSe+0ldriW7RhBnZDP84+71P0fP+UJ0ZyIb4ZUBVfjY4gqWnysYK6Kq nP+ONwsLwgO6Z+AEhyI/bNtcMh09nAlMmtnV0= MIME-Version: 1.0 Received: by 10.231.158.132 with SMTP id f4mr16482721ibx.52.1275856435942; Sun, 06 Jun 2010 13:33:55 -0700 (PDT) Received: by 10.231.190.131 with HTTP; Sun, 6 Jun 2010 13:33:55 -0700 (PDT) Date: Sun, 6 Jun 2010 16:33:55 -0400 Message-ID: From: Nick Rogers To: freebsd-net@freebsd.org Content-Type: text/plain; charset=ISO-8859-1 X-Content-Filtered-By: Mailman/MimeDel 2.1.5 Subject: arp(8) performance w/ many aliases assigned to an interface X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 06 Jun 2010 20:56:34 -0000 I have an 8.0-RELEASE system with 4000 "permanent" ARP entries due to having a network interface (em(4)) configured with 4000 aliases. The "arp -na" command takes what I consider to be an extremely long time to finish (up to 30s on an otherwise unloaded system). I am able to replicate this in a test environment by installing 8.0-RELEASE-amd64 on a VMWare VM w/ 1GB of RAM and a 2GHz CPU. The 4000 aliases/entries is arbitrary, but nicely illustrates the performance problem. The performance is much worse on a real/loaded system. I realize the 4k aliases on an interface is unusual but I have been effectively using this configuration in my network to try and keep my end-users's each on his/her own broadcast domain. The box is a router and I allocate addresses to each user and put each on his/her own subnet with a netmask of /30. If you would like more info on this I can provide it, but it has worked effectively in FreeBSD 6.0-7.2. The slow performance of "arp -na" is an issue for me because I have a web/CGI tool that runs various reports, many of them relying on acquiring the current "ARP table", and the performance of arp(8) makes the web interface extremely slow. I believe the problem was introduced between 7.2 and 8.0, when, as far as I understand, parts of the ARP subsystem were improved. In 7.2, the aliases configured on an interface were not considered ARP entries (at least according to arp(8)), but as of 8.0 they are marked as "permanent" ARP entries and displayed by arp(8), which seems to attribute to the performance problem. I ran the following perl script to setup my test system. This script was run after installing 8.0-RELEASE and adding the bash, perl, and p5-NetAddr-IP packages via pkg_add -r. #!/usr/bin/perl use strict; use diagnostics; use NetAddr::IP; my $interface = 'em1'; my $cidr = '10.0.0.1/18'; # configure the interface with 4000 or so aliases foreach my $na (@{NetAddr::IP->new($cidr)->splitref(30)}) { my $ip = $na->addr(); my $mask = $na->mask(); my $bcast = $na->broadcast()->addr(); my $cmd = "ifconfig $interface inet alias $ip netmask $mask broadcast $bcast"; print STDERR "$cmd\n"; system($cmd); } The results are as follows: [root@ ~]# uname -a FreeBSD .localdomain 8.0-RELEASE FreeBSD 8.0-RELEASE #0: Sat Nov 21 15:02:08 UTC 2009 root@mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC amd64 [root@ ~]# ifconfig -a | wc -l 4113 [root@ ~]# ifconfig -a | head -15 em0: flags=8843 metric 0 mtu 1500 options=9b ether 00:0c:29:65:4d:3e inet 172.16.16.244 netmask 0xffffff00 broadcast 172.16.16.255 media: Ethernet autoselect (1000baseT ) status: active em1: flags=8843 metric 0 mtu 1500 options=9b ether 00:0c:29:65:4d:48 inet 10.0.0.0 netmask 0xfffffffc broadcast 10.0.0.3 inet 10.0.0.4 netmask 0xfffffffc broadcast 10.0.0.7 inet 10.0.0.8 netmask 0xfffffffc broadcast 10.0.0.11 inet 10.0.0.12 netmask 0xfffffffc broadcast 10.0.0.15 inet 10.0.0.16 netmask 0xfffffffc broadcast 10.0.0.19 inet 10.0.0.20 netmask 0xfffffffc broadcast 10.0.0.23 [root@ ~]# time ifconfig -a > /dev/null real 0m0.032s user 0m0.023s sys 0m0.008s [root@ ~]# arp -na | wc -l 4100 [root@ ~]# arp -na | tail -15 ? (10.0.5.80) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.5.48) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.5.16) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.244) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.212) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.180) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.148) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.116) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.84) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.52) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (10.0.1.20) at 00:0c:29:65:4d:48 on em1 permanent [ethernet] ? (172.16.16.1) at 00:50:56:c0:00:08 on em0 [ethernet] ? (172.16.16.2) at 00:50:56:ea:ea:1a on em0 [ethernet] ? (172.16.16.254) at 00:50:56:f2:75:00 on em0 [ethernet] ? (172.16.16.244) at 00:0c:29:65:4d:3e on em0 permanent [ethernet] [root@ ~]# uptime 7:28PM up 42 mins, 2 users, load averages: 0.00, 0.00, 0.00 [root@ ~]# time arp -na > /dev/null real 0m12.761s user 0m2.959s sys 0m9.753s [root@ ~]# Notice that "arp -na" takes about 13s to execute even though there is no other load. This can get a lot worse by a few orders of magnitude on a loaded machine in a production environment, and seems to scale up linearly when more aliases are added to the interface (permanent ARP entries created). I tried the same scenario on 8.1-BETA1 and it still takes a very long time for arp(8) to complete. I was able to isolate the performance bottleneck to a small piece of the arp(8) code. It seems that looking up the interface for an ARP entry is a very heavy operation when that entry corresponds to an alias assigned to the interface. Permanent ARP entries that do not correspond with an interface alias do not seem to cause arp(8) to puke on the interface lookup. The following commands and code diff illustrates how arp(8) can be modified to run a lot faster in this scenario, but obviously the associated interface is no longer printed for each entry. [root@ /usr/src/usr.sbin/arp]# uname -a FreeBSD .localdomain 8.1-BETA1 FreeBSD 8.1-BETA1 #0: Thu May 27 15:03:30 UTC 2010 root@mason.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC amd64 [root@ /usr/src/usr.sbin/arp]# time /usr/sbin/arp -na | wc -l 4100 real 0m14.903s user 0m3.133s sys 0m11.519s [root@ /usr/src/usr.sbin/arp]# pwd /usr/src/usr.sbin/arp [root@ /usr/src/usr.sbin/arp]# !diff diff -ruN arp.c.orig arp.c --- arp.c.orig 2010-06-05 18:25:24.000000000 +0000 +++ arp.c 2010-06-05 18:28:19.000000000 +0000 @@ -562,7 +562,7 @@ const char *host; struct hostent *hp; struct iso88025_sockaddr_dl_data *trld; - char ifname[IF_NAMESIZE]; + //char ifname[IF_NAMESIZE]; int seg; if (nflag == 0) @@ -591,8 +591,8 @@ } } else printf("(incomplete)"); - if (if_indextoname(sdl->sdl_index, ifname) != NULL) - printf(" on %s", ifname); + //if (if_indextoname(sdl->sdl_index, ifname) != NULL) + //printf(" on %s", ifname); if (rtm->rtm_rmx.rmx_expire == 0) printf(" permanent"); else { [root@ /usr/src/usr.sbin/arp]# make clean && make rm -f arp arp.o arp.4.gz arp.8.gz arp.4.cat.gz arp.8.cat.gz Warning: Object directory not changed from original /usr/src/usr.sbin/arp cc -O2 -pipe -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wno-uninitialized -Wno-pointer-sign -c arp.c cc -O2 -pipe -std=gnu99 -fstack-protector -Wsystem-headers -Werror -Wall -Wno-format-y2k -W -Wno-unused-parameter -Wstrict-prototypes -Wmissing-prototypes -Wpointer-arith -Wno-uninitialized -Wno-pointer-sign -o arp arp.o gzip -cn arp.4 > arp.4.gz gzip -cn arp.8 > arp.8.gz [root@ /usr/src/usr.sbin/arp]# time ./arp -na | wc -l 4099 real 0m0.036s user 0m0.015s sys 0m0.021s [root@ /usr/src/usr.sbin/arp]# Notice that 0.036s without the interface lookup is a heck of a lot faster than 14.903s when doing the interface lookup. Is there something that can be done to speedup the call to if_indextoname(), or would it be worthwhile for me to submit a patch that adds the ability to skip the interface lookup as an arp(8) option?