[Cerowrt-devel] cerowrt 3.3.8-17 is released

Dave Taht dave.taht at gmail.com
Thu Aug 16 00:08:50 EDT 2012

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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