Ahhh,  thanks, Sebastian.  Now I understand what you are doing is a stress test.
 
 
 
 
 
 
 
-----Original Message-----
From: "Sebastian Moeller" <moeller0@gmx.de>
Sent: Tuesday, August 21, 2012 1:28am
To: "Marchon" <marchon@gmail.com>
Cc: "dpreed@reed.com" <dpreed@reed.com>, "cerowrt-devel@lists.bufferbloat.net" <cerowrt-devel@lists.bufferbloat.net>
Subject: Re: [Cerowrt-devel] cerowrt 3.3.8-17 is released



Hi there,

again the UDP flood test was not about the cable modem but just about resilience under (extreme) load. So just plain bread and butter functionality of a router, nothing fancy :) As is it causes a mix of very slow processing due to allocation errors and occasional OOM situations and full reboots. IMHO surviving the stress without these unfortunate outcomes would be preferable…


best
 Sebastian

On Aug 20, 2012, at 7:44 PM, Marchon wrote:

> It The Fq_codel settings prevent excess buffering on the push of data out over the cable modem itself / it will prevent unnecessary premature reduction of the  tcp sliding window size further preventing a cascading backlog that ends up further reducing the sliding window and slowing down the overall outbound transfer rate. 
> 
> A buffering problem in the cable modem only happens if you feed it data to quickly. 
> 
> 
> 
> 
> 
> 
> Sent from my iPhone
> 
> On Aug 20, 2012, at 10:33 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*.
>>  
>> How could it?   In order for that to be fixed, you need to manage the buffer in the cable modem itself.
>>  
>> -----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
>> 
>> 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.
>> ##############
>> 
>> use Socket;
>> use strict;
>> 
>> if ($#ARGV != 3) {
>> print "flood.pl <ip> <port> <size> <time>\n\n";
>> print " port=0: use random ports\n";
>> print " size=0: use random size between 64 and 1024\n";
>> print " time=0: continuous flood\n";
>> exit(1);
>> }
>> 
>> my ($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 192.168.100.1 0 1024 240
>> or 
>> 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… 
>> 
>> best
>> Sebastian
>> 
>> 
>> 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@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@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
>> >> 
>> >> 
>> >> 
>> >> 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@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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