[Cake] Advantages to tightly tuning latency

Luca Muscariello muscariello at ieee.org
Wed Apr 22 11:28:06 EDT 2020

On Wed, Apr 22, 2020 at 4:48 PM Dave Taht <dave.taht at gmail.com> wrote:

> On Wed, Apr 22, 2020 at 2:04 AM Luca Muscariello <muscariello at ieee.org>
> wrote:
> >
> >
> >
> > On Wed, Apr 22, 2020 at 12:44 AM Dave Taht <dave.taht at gmail.com> wrote:
> >>
> >> On Tue, Apr 21, 2020 at 3:33 PM Jonathan Morton <chromatix99 at gmail.com>
> wrote:
> >> >
> >> > > On 22 Apr, 2020, at 1:25 am, Thibaut <hacks at slashdirt.org> wrote:
> >> > >
> >> > > My curiosity is piqued. Can you elaborate on this? What does
> free.fr do?
> >> >
> >> > They're a large French ISP.  They made their own CPE devices, and
> debloated both them and their network quite a while ago.  In that sense, at
> least, they're a model for others to follow - but few have.
> >> >
> >> >  - Jonathan Morton
> >>
> >> they are one of the few ISPs that insisted on getting full source code
> >> to their DSL stack, and retained the chops to be able to modify it. I
> >> really admire their revolution v6 product. First introduced in 2010,
> >> it's been continuously updated, did ipv6 at the outset, got fq_codel
> >> when it first came out, and they update the kernel regularly. All
> >> kinds of great features on it, and ecn is enabled by default for those
> >> also (things like samba). over 3 million boxes now I hear....
> >>
> >> with <1ms of delay in the dsl driver, they don't need to shape, they
> >> just run at line rate using three tiers of DRR that look a lot like
> >> cake. They shared their config with me, and before I lost heart for
> >> future internet drafts, I'd stuck it here:
> >>
> >>
> https://github.com/dtaht/bufferbloat-rfcs/blob/master/home_gateway_queue_management/middle.mkd
> >>
> >> Occasionally they share some data with me. Sometimes I wish I lived in
> >> paris just so I could have good internet! (their fiber offering is
> >> reasonably buffered (not fq_codeled) and the wifi... maybe I can get
> >> them to talk about what they did)
> >>
> >> When free.fr shipped fq_codel 2 months after we finalized it, I
> >> figured the rest of the world was only months behind. How hard is it
> >> to add 50 lines of BQL oriented code to a DSL firmware?
> >>
> >
> > Free has been using SFQ since 2005 (if I remember well).
> > They announced the wide deployment of SFQ in the free.fr newsgroup.
> > Wi-Fi in the free.fr router was not as good though.
> They're working on it. :)
> > In Paris there is a lot of GPON now that is replacing DSL. But there is
> > a nation-wide effort funded by local administrations to get fiber
> > everywhere. There are small towns in the countryside with fiber.
> > Public money has made, and is making that possible.
> > There is still a little of Euro-DOCSIS, but frankly compared to fiber
> > it has no chance to survive.
> I am very, very happy for y'all. Fiber has always been the sanest
> thing. Is there
> a SPF+ gpon card yet I can plug into a convention open source router yet?
> >
> > I currently have 2Gbps/600Mbps access with orange.fr and free.fr has a
> subscription
> > at 10Gbps GPON. I won't tell you the price because you may feel depressed
> > compared to other countries where prices are much higher.
> I'd emigrate!!!
> > The challenge becomes to keep up with these link rates in software
> > as there is a lot of hardware offloading.

I just meant that these routers tend to use HW offloading
and kernel qdiscs may be bypassed.

> At this point, I kind of buy the stanford sqrt(bdp) argument. All you
> really need for gigE+ fiber access to work well
> for most modern traffic is a fairly short fifo (say, 20ms). Any form
> of FQ would help but be hardly noticible. I think
> there needs to be work on the hop between the internet and the
> subscriber...
> Web traffic is dominated by RTT above 40mbit (presently).
> streaming video traffic - is no more than 20Mbit, and your occasional
> big download is a dozen big streams that would
> bounce off a short fifo well.
> gbit access to the home is (admittedly glorious, wonderful!) overkill
> for all present forms of traffic.
> I'm pretty sure if I had gig fiber I could come up with a way to use
> it up (exiting the cloud entirely comes to mind), but
> lacking new applications that demand that much bandwidth...
> I of course, would like to see lola ( https://lola.conts.it/ ) finally
> work, and videoconferencing and game stream with high rates and faster
> (even raw) encoding also has potential to reduce e2e latencies
> enormously at that layer.
> >
> > As soon as 802.11ax becomes the norm, software scheduling will become
> > a challenge.
> Do you mean in fiber or wireless? wireless is really problematic at ANY
> speed.

I meant that software scheduling becomes a challenge for the same
reason as above. Increase in total throughput of the box
will call for hardware offloading and kernel qdisc may be bypassed.

It is not a challenge per se, it is a challenge because traffic
may not be managed by the kernel.

> at gfiber, the buffering moved to the wifi, and there are other
> problems that really impact achievable bandwidth. When I was last in
> paris, I could "hear" 300+ access points from my apt, and could only
> get 100-200kbit per second out of the wireless n ap I had, unless I
> cheated and stuck my traffic in the VI queue. A friend of mine there,
> couldn't even get wifi across the room! Beacons ate into a lot of the
> available
> bandwidth. Since 5ghz (and soon 6ghz - is 6E a thing in france) is
> shorter range I'm hoping that's got better, but with
> 802.11ac and ax peeing on half the wifi spectrum by default, I imagine
> achievable rates in high density locations with many APs will be very
> low... and very jittery... and thus still require good ATF, fq, and
> aqm technologies.
> I have high hopes for OFDMA and DU but thus far haven't found an AP
> doing it. I'm not sure what to do about the beaconing problem except
> offer a free tradein to all my neighbors still emitting G style
> frames....
> And in looking over some preliminary code for the mt76 ax chip, I
> worry about both bad design of the firmware, and
> insufficient resources on-chip to manage well.
> How is the 5G rollout going in france?

Good question. I've just seen a speed test at Gbps on a phone
which can drain your battery in less than 5 minutes. Amazing tech!

> I recently learned that much of japan is... wait for it... wimax.
> >
> > Luca
> --
> Make Music, Not War
> Dave Täht
> CTO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-831-435-0729
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