From owner-freebsd-stable@FreeBSD.ORG Sun Jun 6 03:16:30 2010 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 2AF73106566B for ; Sun, 6 Jun 2010 03:16:30 +0000 (UTC) (envelope-from jdc@koitsu.dyndns.org) Received: from qmta13.westchester.pa.mail.comcast.net (qmta13.westchester.pa.mail.comcast.net [76.96.59.243]) by mx1.freebsd.org (Postfix) with ESMTP id CB8E08FC12 for ; Sun, 6 Jun 2010 03:16:29 +0000 (UTC) Received: from omta01.westchester.pa.mail.comcast.net ([76.96.62.11]) by qmta13.westchester.pa.mail.comcast.net with comcast id STA51e0030EZKEL5DTGVBz; Sun, 06 Jun 2010 03:16:29 +0000 Received: from koitsu.dyndns.org ([98.248.46.159]) by omta01.westchester.pa.mail.comcast.net with comcast id STGU1e0073S48mS3MTGVnw; Sun, 06 Jun 2010 03:16:29 +0000 Received: by icarus.home.lan (Postfix, from userid 1000) id 62EE09B418; Sat, 5 Jun 2010 20:16:27 -0700 (PDT) Date: Sat, 5 Jun 2010 20:16:27 -0700 From: Jeremy Chadwick To: Nick Rogers Message-ID: <20100606031627.GA4742@icarus.home.lan> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-06-14) Cc: FreeBSD STABLE Subject: Re: arp -na performance w/ many permanent entries X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 06 Jun 2010 03:16:30 -0000 On Sat, Jun 05, 2010 at 09:48:01PM -0400, Nick Rogers wrote: > On Mon, May 31, 2010 at 10:54 PM, Nick Rogers wrote: > > > > > [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). > > > > Is this a reasonable problem that can be fixed/improved, or am I stuck with > > the slow arp -na output? Any help or comments is greatly appreciated. > > > > 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? This might be a better question for either freebsd-net or freebsd-hackers. I should warn you in advance that you might receive a bit of flack given that you have over 4000 IP aliases assigned to an interface. Explaining your setup may also help people understand why it is you need what you do. -- | Jeremy Chadwick jdc@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB |