[Cake] lockup with cake and veth

Georgios Amanakis gamanakis at gmail.com
Fri Jul 6 09:34:15 EDT 2018

Thank you both for the great work!
I will give it a try, too.


On Fri, Jul 6, 2018, 9:29 AM Toke Høiland-Jørgensen <toke at toke.dk> wrote:

> Pete Heist <pete at heistp.net> writes:
> > I don’t know if we want to call this an issue, but...
> >
> > I’m seeing a lockup with cake (and also sfq, but not either pfifo or
> > fq_codel), when run over veth devices. Two network namespaces are
> > created, one for client and one for server, each with one veth device.
> > Netem is added as the root qdisc with a delay of 1ms, and a leaf qdisc
> > may be added. Lockups occur on my box when the leaf qdisc is either
> > cake or sfq, and I'm running flent’s tcp_ndown test with >= 4 download
> > streams. Note that I happen to be running on a quad-core.
> >
> > - If no leaf qdisc is added below netem, no lockup occurs.
> > - If either pfifo or fq_codel is added below netem, no lockup occurs.
> > - If either cake or sfq is the leaf, the lockup occurs.
> >
> > The symptoms (lockup with >= 4 streams on a quad-core box), and the
> > fact that it occurs with both cake and sfq, make me think that it may
> > simply have to do with the code not being re-entrant, which may be the
> > case for veth, and this is just by design? maybe something that we
> > should consider fixing but wouldn’t be a show-stopper? But that should
> > be confirmed.
> >
> > I’ll keep investigating, but am sharing the scripts I’m running
> > meanwhile in case anyone else wants to look. See README.txt in the
> > attached...
> Thanks for investigating! I'll take a look later. The fact that it
> happens with sfq as well means it's probably not cake-specific, though,
> so I don't think we should hold off on the upstream submission until
> we've figured it out. Using leaf qdiscs with netem has been dodgy for a
> while IIRC...
> -Toke
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