[Bloat] beating the drum for BQL

Dave Taht dave.taht at gmail.com
Fri Aug 24 14:43:01 EDT 2018

On Fri, Aug 24, 2018 at 10:30 AM Dave Taht <dave.taht at gmail.com> wrote:
> On Fri, Aug 24, 2018 at 10:13 AM Pete Heist <pete at heistp.net> wrote:
> >
> >
> > On Aug 23, 2018, at 10:26 AM, Pete Heist <pete at heistp.net> wrote:
> >
> > On Aug 23, 2018, at 2:49 AM, Dave Taht <dave.taht at gmail.com> wrote:
> >
> > I had a chance to give a talk at broadcom recently, slides here:
> >
> > http://flent-fremont.bufferbloat.net/~d/broadcom_aug9.pdf
> >
> >
> > Thanks for sharing, this is really useful, raising awareness where it matters. Quite a bit of content... :)
> >
> > Ubiquiti needs some work getting this into more of their products (EdgeMAX in particular). A good time to lobby for this might be, well a couple months ago, as they’re producing alpha builds for their upcoming 2.0 release with kernel 4.9 and new Cavium/Mediatek/Octeon SDKs. I just asked about the status in the EdgeRouter Beta forum, in case it finds the right eyes before the release:
> >
> > https://community.ubnt.com/t5/EdgeRouter-Beta/BQL-support/m-p/2466657
> >
> >
> > This started a discussion, and no, so far it looks like there’s no BQL support in the upcoming 2.0 release.
> >
> > For my own benefit, re-reading the original patch series comment (https://lwn.net/Articles/469652/) makes it sound like BQL is useful even without AQM (original benchmarks were done with straight pfifo_fast). I didn’t realize this, actually. If anything incorrect about BQL was said in this discussion, correct us, please… :)
> yes, bql is very useful even with pfifo fast. without BQL I doubt the
> internet would be scaling as it is today in the dc, or on the smaller
> hosts and devices that support it. It's in the mvneta, it's in the
> ar71xx, with documented results there that I could dig up.  (tho:
> things like tsq are helping and mask the problem on simple tests) The
> experiment I documented on the slides that kicked off this thread and
> the other experiment on the systemd bug, easily show the benefit on
> hosts forwarding packets (be they from local applications, coming from
> various sources like docker containers, etc), and anyone can show what
> goes wrong if you disable BQL nowadays, basically restoring linux-3.3
> behavior, with a very simple test:
> For I in /sys/class/net/your_device/queues/tx*/byte_queue_limits/limit_min
> do
>      echo 10000000 > $I
> done
> so long as you run enough kinds of flows that don't engage TSQ.
> However, in the edgerouter w/offloads case all that part of the stack
> has been short circuited into the offload engine. I don't know how
> much buffering is in there on the new firmware, I'd done a few tests
> on it in the old days, showing it to be around 10ms at gigE but even
> that memory is kind of vague (the easy test here is slam two ports
> into one), and for all I know the new firmware is worse, without going
> back to track this new release. (I do have a few edgerouters but they
> are all in production)
> There was also a paper on BQL a few years back that I can dig up....

The only academic analysis so of BQL i knew of was this: "bufferbloat
systemic analysis": http://200 dot 131 dot 219 dot
61/publications/2014/its2014_bb.pdf - note that bufferbloat.net's
filters don't let me post numeric urls and you can find the paywalled
versions by searching for that title on google scholar. Or on sci-hub.

I found that again by re-reading my preso to sigcomm 2014  "The value
of repeatable experiments and negative results" -
https://conferences.sigcomm.org/sigcomm/2014/doc/slides/137.pdf )
which - in addition to providing some value-able history and links to
the bufferbloat, fq, and aqm efforts, is really one of my best rants
*ever* aimed at the academic research and publication process.

I enjoyed writing that, and giving the preso *a lot*. For some reason
or another sigcomm has not invited me back. :)

> > Pete
> >
> --
> Dave Täht
> CEO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-669-226-2619


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

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