[Cake] Advantages to tightly tuning latency

Wed Apr 22 10:48:43 EDT 2020

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.

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.

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?

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