Re: [bmwg] Benjamin Kaduk's No Objection on draft-ietf-bmwg-sdn-controller-benchmark-meth-08: (with COMMENT)

Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com> Thu, 19 April 2018 17:02 UTC

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From: Spencer Dawkins at IETF <spencerdawkins.ietf@gmail.com>
Date: Thu, 19 Apr 2018 12:02:45 -0500
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To: Benjamin Kaduk <kaduk@mit.edu>
Cc: Sarah B <sbanks@encrypted.net>, draft-ietf-bmwg-sdn-controller-benchmark-meth@ietf.org, bmwg-chairs@ietf.org, ALFRED MORTON <acmorton@att.com>, "Bhuvan (Veryx Technologies)" <bhuvaneswaran.vengainathan@veryxtech.com>, The IESG <iesg@ietf.org>, bmwg@ietf.org
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Subject: Re: [bmwg] Benjamin Kaduk's No Objection on draft-ietf-bmwg-sdn-controller-benchmark-meth-08: (with COMMENT)
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This is Benjamin's ballot thread, but ...

On Thu, Apr 19, 2018 at 11:41 AM, Benjamin Kaduk <kaduk@mit.edu> wrote:

> On Thu, Apr 19, 2018 at 09:32:38AM -0700, Sarah B wrote:
> > Hi Benjamin,
> >       Thanks for your review. A few comments inline below with SB//
> >
> > Thanks
> > Sarah
> > >
> > > ----------------------------------------------------------------------
> > > COMMENT:
> > > ----------------------------------------------------------------------
> > >
> > > In the Abstract:
> > >
> > >   This document defines the methodologies for benchmarking control
> > >   plane performance of SDN controllers.
> > >
> > > Why "the" methodologies?   That seems more authoritative than is
> > > appropriate in an Informational document.
> > >
> >
> > Sure, we can remove this.
>
> (I probably should have explicitly said that "a methodology" is
> fine.)
>
> > >
> > > Thank you for adding consideration to key distribution in Section
> > > 4.4, as noted by the secdir review.  But insisting on having key
> > > distribution done prior to testing gives the impression that keys
> > > are distributed once and updated never, which has questionable
> > > security properties.  Perhaps there is value in doing some testing
> > > while rekeyeing is in progress?
> >
> > We'll discuss internally.. the goal here wasn't to test rekeying, which
> is why the test doesn't call for anything other than doing the distribution
> prior to the test, and remember, this is lab testing; this isn't what
> happens on a live network, but it's an interesting point, and we'll discuss.
>
> Okay.  I'm just approaching this from a "social norms" perspective
> (regarding expectations that re-keying will be done), but I
> definitely understand that there is less need for benchmarking
> rekeying performance than the cases already covered.
>
> > >
> > > I agree with others that the statistical methodology is not clearly
> > > justified, such as the sample size of 10 in Section 4.7 (with no
> > > consideration for sample relative variance), use of sample vs.
> > > population veriance, etc.
> >
> > As a draft, we aren't saying you only have to do 10; it's been a point
> of discussion in BMWG for some time, what number do you put? We haven't
> always found a happy medium to this. We're suggesting you perform the test
> 10 times, but there's nothing that stops a tester from making that <n>
> times; for example, 100 times. It's important to note how many times the
> test was performed and move on. We can clarify this text to reflect that,
> if it helps. However, note, BMWG is about repeatability, and that was the
> goal here.
>
> Well, there's a huge amount of literature (and, e.g., textbooks) on
> statistical anlaysis and how to decide that a series of measurements
> has converged on a stable result.  So it might be better to just say
> that benchmarkers must ensure that the data has converged and note
> that this will require running many repeated trials, but not
> necessarily list a specific value.


FWIW, that's the kind of thing I was asking about in my own ballot. If 10
repetitions has been a good heuristic in testing so far, that could be
worth saying, but if people are going to have to look at results and figure
out whether they've repeated a test often enough, you might as well put it
in those terms.

IMO, of course.

Spencer