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From: Sebastian Moeller <moeller0@gmx.de>
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Date: Mon, 20 Aug 2012 11:24:12 -0700
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To: Dave Taht <dave.taht@gmail.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 Dave,

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)

#!/usr/bin/perl
##############

# 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
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));}

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

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=


best
	Sebastian


On Aug 15, 2012, at 9:08 PM, Dave Taht wrote:

> 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!"