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From: Sebastian Moeller <moeller0@gmx.de>
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To: dpreed@reed.com
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Cc: cerowrt-devel@lists.bufferbloat.net
Subject: Re: [Cerowrt-devel] cerowrt 3.3.8-17 is released
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Hi,


On Aug 20, 2012, at 7:33 PM, dpreed@reed.com wrote:

> I'm confused.  Fq_codel does not (to my knowledge) fix bufferbloat *in =
your cable modem*  or *in the CMTS head-end*.
> =20
> How could it?   In order for that to be fixed, you need to manage the =
buffer in the cable modem itself.

	Oh, I agree; the quoted mail's implicit topic was a report in my =
ongoing struggle with cerowrt's instability under load. Dave has a =
number of issues in the cerowrt bug tracker to that regard as well. I =
had just figured out how to UDP-stress my router without having to use =
the web service I used before. UDP flooding my modem is not intended to =
tell me anything about the CPE or CMTS, I just need an IP under my =
control on the other side of the router that I could direct the load =
test to that would not consider this an DoS attempt, hence my own cable =
modem as endpoint=85
	I have the feeling that a home-router is so much more useful if =
it does not crash or reboot itself if just asked to do its job, namely =
routing of packets. And cerowrt is close to that goal if the memory =
allocation issues can be fixed, at least that is my hope=85 =46rom my =
layman's persecutive it sounds so simple, just drop all incoming packets =
that the router will not be able to handle and keep hanging in there =
awaiting better times with less traffic. So I am fine with the router =
not doing anything useful during the UDP flood, but I sure hope it =
recovers quickly thereafter.

best
	Sebastian


> =20
> -----Original Message-----
> From: "Sebastian Moeller" <moeller0@gmx.de>
> Sent: Monday, August 20, 2012 2:24pm
> To: "Dave Taht" <dave.taht@gmail.com>
> Cc: cerowrt-devel@lists.bufferbloat.net
> Subject: Re: [Cerowrt-devel] cerowrt 3.3.8-17 is released
>=20
> Hi Dave,
>=20
> so I went to play around with this a bit more. I turned to UDP =
flooding my cable modem through the router and this surely allows me to =
create enough load on the wndr3700v2 to cause the allocation errors and =
as a "bonus" also to drive the router to reboot (driven by the watchdog =
timer?). Here is the script I used over 5G wireless (from =
http://blog.ioshints.info/2008/03/udp-flood-in-perl.html)
>=20
> #!/usr/bin/perl
> ##############
>=20
> # udp flood.
> ##############
>=20
> use Socket;
> use strict;
>=20
> if ($#ARGV !=3D 3) {
> print "flood.pl <ip> <port> <size> <time>\n\n";
> print " port=3D0: use random ports\n";
> print " size=3D0: use random size between 64 and 1024\n";
> print " time=3D0: continuous flood\n";
> exit(1);
> }
>=20
> my ($ip,$port,$size,$time) =3D @ARGV;
>=20
> my ($iaddr,$endtime,$psize,$pport);
>=20
> $iaddr =3D inet_aton("$ip") or die "Cannot resolve hostname $ip\n";
> $endtime =3D time() + ($time ? $time : 1000000);
>=20
> socket(flood, PF_INET, SOCK_DGRAM, 17);
>=20
>=20
> print "Flooding $ip " . ($port ? $port : "random") . " port with " .=20=

> ($size ? "$size-byte" : "random size") . " packets" .=20
> ($time ? " for $time seconds" : "") . "\n";
> print "Break with Ctrl-C\n" unless $time;
>=20
> for (;time() <=3D $endtime;) {
> $psize =3D $size ? $size : int(rand(1024-64)+64) ;
> $pport =3D $port ? $port : int(rand(65500))+1;
>=20
> send(flood, pack("a$psize","flood"), 0, pack_sockaddr_in($pport, =
$iaddr));}
>=20
> called as either
> udp_flood.pl 192.168.100.1 0 1024 240
> or=20
> udp_flood.pl 192.168.100.1 32000 1024 240
>=20
> The first version with randomized port number spreads the load nicely =
over many fq_codel bins/flows and seems slightly more likely to cause =
allocation errors and reboots than the 2nd invocation which restricts =
itself to port 32000 and presumably just one flow.
> I wonder how to make cerowrt survive this kind of stress test=85=20
>=20
> best
> Sebastian
>=20
>=20
> On Aug 15, 2012, at 9:08 PM, Dave Taht wrote:
>=20
> > re: ath: skbuff alloc of size 1926 failed
> >=20
> > as for the ath skbuff problem, I've seen that a lot. I had put hard
> > packet limits (~600) on fq_codel in -11 and prior that were too low
> > and it mostly went away, but I hit tail drop behavior everywhere,
> > instead of codel behavior. What I have now (typically 1200) may well
> > be too high, but not as overly high as the default (10k packets).
> > There may be another means of increasing the size of that slab pool =
or
> > making it less onerous.
> >=20
> > I would like it if codel "kicked in" earlier than it currently does.
> > The code in ns2 is currently using half the period that the linux =
code
> > is. This would control things better, or so I hope (planning on =
trying
> > this as I get time)
> >=20
> > I am also considering means of artificially upscaling the drop
> > scheduler when we get close to queue limits.
> >=20
> > See some discussions on the codel list for these issues. (sims are
> > easier to deal with than cerowrt, too!)
> >=20
> > as for bind, it should be automagically restarted from xinetd, no =
need
> > to fiddle with anything. However, since you are already under =
massive
> > memory pressure, it may well fail to start up that way, too. At the
> > moment, I've largely given up on bind on anything but a more core =
home
> > gw, and am running dnsmasq on everything (3700v2, picostations,
> > nanostations) but the 3800s. (and the ones I run it on, aren't being
> > used for wifi right now).
> >=20
> > Lastly: Swap space won't help you on exhausting kernel limits.
> >=20
> > I'm glad you can reproduce the ath: slab problem - I can get it too =
at
> > high rates using netperf over wifi. I will try a 3700v2 with and
> > without bind to see if it's still there in 3.3.8-17. In the meantime
> > if anyone knows how to get more allocations in that (2048? 4096?) =
slab
> > by default, perhaps that will help?
> >=20
> >=20
> >=20
> > On Wed, Aug 15, 2012 at 10:23 AM, Sebastian Moeller =
<moeller0@gmx.de> wrote:
> >> Hi Dave,
> >>=20
> >> great work, as always I upgraded my production router to the latest =
and greatest (since I only have one router=85). And it works quite well =
for normal usage=85
> >> Netalyzr reports around 2800ms seconds of uplink buffering, yet =
saturating the uplink does not affect ping times to a remote target =
noticeably, basically the same as for all codellized ceo versions I =
tested so far...
> >>=20
> >> Some notes and a question:
> >> I noticed that even given plenty of swap space (1GB on a usb =
stick), using http://broadband.mpi-sws.org/residential/ to exercise UDP =
stress (on the uplink I assume) I can easily produce (I run the test =
from a macosx via 5GHz wireless over 1.5 yards):
> >> Aug 15 01:16:29 nacktmulle kern.err kernel: [175395.132812] ath: =
skbuff alloc of size 1926 failed
> >> (and plenty of those=85).
> >> What then happens is that the OOM killer will aim for bind =
(reasonable since it is the largest single process) and kill it. When I =
try to restart bind by:
> >> root@nacktmulle:~# /etc/rc.d/S47namedprep start
> >> root@nacktmulle:~# /etc/rc.d/S48named restart
> >> Stopping isc-bind
> >> /etc/chroot/named//var/run/named/named.pid not found, trying brute =
force
> >> killall: named: no process killed
> >> Kicking isc-bind in xinetd
> >> rndc: connect failed: 127.0.0.1#953: connection refused
> >> And bind does not start again and the router becomes less than =
useful. Now I assume I am doing something wrong, but what, if you have =
any idea how to solve this short of a reboot of the router (my current =
method) I would be happy to learn
> >>=20
> >>=20
> >>=20
> >> best regards
> >> sebastian
> >>=20
> >> On Aug 12, 2012, at 11:08 PM, Dave Taht wrote:
> >>=20
> >>> I'm too tired to write up a full set of release notes, but I've =
been
> >>> testing it all day,
> >>> and it looks better than -10 and certainly better than -11, but I =
won't know
> >>> until some more folk sit down and test it, so here it is.
> >>>=20
> >>> http://huchra.bufferbloat.net/~cero1/3.3/3.3.8-17/
> >>>=20
> >>> fresh merge with openwrt, fix to a bind CVE, fixes for 6in4 and =
quagga
> >>> routing problems,
> >>> and a few tweaks to fq_codel setup that might make voip better.
> >>>=20
> >>> Go forth and break things!
> >>>=20
> >>> In other news:
> >>>=20
> >>> Van Jacobson gave a great talk about bufferbloat, BQL, codel, and =
fq_codel
> >>> at last week's ietf meeting. Well worth watching. At the end he =
outlines
> >>> the deployment problems in particular.
> >>>=20
> >>> =
http://recordings.conf.meetecho.com/Recordings/watch.jsp?recording=3DIETF8=
4_TSVAREA&chapter=3Dpart_3
> >>>=20
> >>> Far more interesting than this email!
> >>>=20
> >>>=20
> >>> --
> >>> Dave T=E4ht
> >>> http://www.bufferbloat.net/projects/cerowrt/wiki - "3.3.8-17 is =
out
> >>> with fq_codel!"
> >>> _______________________________________________
> >>> Cerowrt-devel mailing list
> >>> Cerowrt-devel@lists.bufferbloat.net
> >>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >>=20
> >=20
> >=20
> >=20
> > --=20
> > Dave T=E4ht
> > http://www.bufferbloat.net/projects/cerowrt/wiki - "3.3.8-17 is out
> > with fq_codel!"
>=20
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