[openstack-dev] [Neutron][qa] Parallel testing update

Salvatore Orlando sorlando at nicira.com
Mon Jan 6 20:24:26 UTC 2014

This thread is starting to get a bit confusing, at least for people with a
single-pipeline brain like me!

I am not entirely sure if I understand correctly Isaku's proposal
concerning deferring the application of flow changes.
I think it's worth discussing in a separate thread, and a supporting patch
will help as well; I think that in order to avoid unexpected behaviours,
vlan tagging on the port and flow setup should always be performed at the
same time; if we get a much better performance using a mechanism similar to
iptables' defer_apply, then we should it.

Regarding rootwrap. This 6x slowdown, while proving that rootwrap imposes a
non-negligible overhead, it should not be used as a sort of proof that
rootwrap makes things 6 times worse! What I've been seeing on the gate and
in my tests are ALRM_CLOCK errors raised by ovs commands, so rootwrap has
little to do with it.

Still, I think we can say that rootwrap adds about 50ms to each command,
becoming particularly penalising especially for 'fast' commands.
I think the best things to do, as Joe advices, a test with rootwrap
disabled on the gate - and I will take care of that.

On the other hand, I would invite community members picking up some of the
bugs we've registered for 'less frequent' failures observed during parallel
testing; especially if you're coming to Montreal next week.


On 6 January 2014 20:31, Jay Pipes <jaypipes at gmail.com> wrote:

> On Mon, 2014-01-06 at 11:17 -0800, Joe Gordon wrote:
> >
> >
> >
> > On Mon, Jan 6, 2014 at 10:35 AM, Jay Pipes <jaypipes at gmail.com> wrote:
> >         On Mon, 2014-01-06 at 09:56 -0800, Joe Gordon wrote:
> >
> >         > What about it? Also those numbers are pretty old at this
> >         point. I was
> >         > thinking disable rootwrap and run full parallel tempest
> >         against it.
> >
> >
> >         I think that is a little overkill for what we're trying to do
> >         here. We
> >         are specifically talking about combining many utils.execute()
> >         calls into
> >         a single one. I think it's pretty obvious that the latter will
> >         be better
> >         performing than the first, unless you think that rootwrap has
> >         no
> >         performance overhead at all?
> >
> >
> > mocking out rootwrap with straight sudo, is a very quick way to
> > approximate the performance benefit of combining many utlils.execute()
> > calls together (at least rootwrap wise).  Also  it would tell us how
> > much of the problem is rootwrap induced and how much is other.
> Yes, I understand that, which is what the article I linked earlier
> showed?
> % time sudo ip link >/dev/null
> sudo ip link > /dev/null  0.00s user 0.00s system 43% cpu 0.009 total
> % sudo time quantum-rootwrap /etc/quantum/rootwrap.conf ip link
> > /dev/null
> quantum-rootwrap /etc/quantum/rootwrap.conf ip link  > /dev/null  0.04s
> user 0.02s system 87% cpu 0.059 total
> A very tiny, non-scientific simple indication that rootwrap is around 6
> times slower than a simple sudo call.
> Best,
> -jay
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