[Cerowrt-devel] cerowrt 3.3.8-17 is released

Sebastian Moeller moeller0 at gmx.de
Mon Aug 20 14:24:12 EDT 2012

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)


# udp flood.
use Socket;
use strict;
if ($#ARGV != 3) {
  print "flood.pl <ip> <port> <size> <time>\n\n";
  print " port=0: use random ports\n";
  print " size=0: use random size between 64 and 1024\n";
  print " time=0: continuous flood\n";
my ($ip,$port,$size,$time) = @ARGV;
my ($iaddr,$endtime,$psize,$pport);
$iaddr = inet_aton("$ip") or die "Cannot resolve hostname $ip\n";
$endtime = time() + ($time ? $time : 1000000);
socket(flood, PF_INET, SOCK_DGRAM, 17);

print "Flooding $ip " . ($port ? $port : "random") . " port with " . 
  ($size ? "$size-byte" : "random size") . " packets" . 
  ($time ? " for $time seconds" : "") . "\n";
print "Break with Ctrl-C\n" unless $time;
for (;time() <= $endtime;) {
  $psize = $size ? $size : int(rand(1024-64)+64) ;
  $pport = $port ? $port : int(rand(65500))+1;
  send(flood, pack("a$psize","flood"), 0, pack_sockaddr_in($pport, $iaddr));}

called as either
udp_flood.pl 0 1024 240
udp_flood.pl 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… 


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

> re: ath: skbuff alloc of size 1926 failed
> 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.
> 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)
> I am also considering means of artificially upscaling the drop
> scheduler when we get close to queue limits.
> See some discussions on the codel list for these issues. (sims are
> easier to deal with than cerowrt, too!)
> 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).
> Lastly: Swap space won't help you on exhausting kernel limits.
> 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?
> On Wed, Aug 15, 2012 at 10:23 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:
>> Hi Dave,
>> great work, as always I upgraded my production router to the latest and greatest (since I only have one router…). And it works quite well for normal usage…
>> 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...
>> 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…).
>> 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 at nacktmulle:~# /etc/rc.d/S47namedprep start
>> root at 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: 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
>> best regards
>>        sebastian
>> On Aug 12, 2012, at 11:08 PM, Dave Taht wrote:
>>> 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.
>>> http://huchra.bufferbloat.net/~cero1/3.3/3.3.8-17/
>>> 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.
>>> Go forth and break things!
>>> In other news:
>>> 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.
>>> http://recordings.conf.meetecho.com/Recordings/watch.jsp?recording=IETF84_TSVAREA&chapter=part_3
>>> Far more interesting than this email!
>>> --
>>> Dave Täht
>>> http://www.bufferbloat.net/projects/cerowrt/wiki - "3.3.8-17 is out
>>> with fq_codel!"
>>> _______________________________________________
>>> Cerowrt-devel mailing list
>>> Cerowrt-devel at lists.bufferbloat.net
>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> -- 
> Dave Täht
> http://www.bufferbloat.net/projects/cerowrt/wiki - "3.3.8-17 is out
> with fq_codel!"

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