[Cake] [Bloat] Really getting 1G out of ISP?

Dave Taht dave.taht at gmail.com
Tue Jul 6 22:26:47 EDT 2021

On Tue, Jul 6, 2021 at 3:32 PM Aaron Wood <woody77 at gmail.com> wrote:
> I'm running an Odyssey from Seeed Studios (celeron J4125 with dual i211), and it can handle Cake at 1Gbps on a single core (which it needs to, because OpenWRT's i211 support still has multiple receive queues disabled).

Not clear if that is shaped or not? Line rate is easy on processors of
that class or better, but shaped?

some points:

On inbound shaping especially it it still best to lock network traffic
to a single core in low end platforms.

Cake itself is not multicore, although the design essentially is. We
did some work towards trying to make it shape across multiple cores
and multiple hardware queues. IF the locking contention could be
minimized (RCU) I felt it possible for a win here, but a bigger win
would be to eliminate "mirred" from the ingress path entirely.

Even multiple transmit queues remains kind of dicy in linux, and
actually tend to slow network processing in most cases I've tried at
gbit line rates. They also add latency, as (1) BQL is MIAD, not AIMD,
so it stays "stuck" at a "good" level for a long time, AND 2) each hw
queue gets an additive fifo at this layer, so where, you might need
only 40k to keep a single hw queue busy, you end up with 160k with 4
hw queues. This problem is getting worse and worse (64 queues are
common in newer hardware, 1000s in really new hardware) and a revisit
to how BQL does things in this case would be useful. Ideally it would
share state (with a cross core variable and atomic locks) as to how
much total buffering was actually needed "down there" across all the
queues, but without trying it, I worry that that would end up costing
a lot of cpu cycles.

Feel free to experiment with multiple transmit queues locked to other
cores with the set-affinity bits in /proc/interrupts. I'm sure these
MUST be useful on some platform, but I think most of the use for
multiple hw queues is when a locally processing application  is
getting the data, not when it is being routed.

Ironically, I guess, the shorter your queues the higher likelihood a
given packet will remain in l2 or even l1 cache.

> On Tue, Jun 22, 2021 at 12:44 AM Giuseppe De Luca <dropheaders at gmx.com> wrote:
>> Also a PC Engines APU4 will do the job
>> (https://inonius.net/results/?userId=17996087f5e8 - this is a
>> 1gbit/1gbit, with Openwrt/sqm-scripts set to 900/900.  ISP is Sony NURO
>> in Japan). Will follow this thread to know if some interesting device
>> popup :)
>> https://inonius.net/results/?userId=17996087f5e8
>> On 6/22/2021 6:12 AM, Sebastian Moeller wrote:
>> >
>> > On 22 June 2021 06:00:48 CEST, Stephen Hemminger <stephen at networkplumber.org> wrote:
>> >> Is there any consumer hardware that can actually keep up and do AQM at
>> >> 1Gbit.
>> >          Over in the OpenWrt forums the same question pops up routinely once per week. The best answer ATM seems to be a combination of a raspberry pi4B with a decent USB3 gigabit ethernet dongle, a managed switch and any capable (OpenWrt) AP of the user's liking. With 4 arm A72 cores the will traffic shape up to a gigabit as reported by multiple users.
>> >
>> >
>> >> It seems everyone seems obsessed with gamer Wifi 6. But can only do
>> >> 300Mbit single
>> >> stream with any kind of QoS.
>> > IIUC most commercial home routers/APs bet on offload engines to do most of the heavy lifting, but as far as I understand only the NSS cores have a shaper and fq_codel module....
>> >
>> >
>> >> It doesn't help that all the local ISP's claim 10Mbit upload even with
>> >> 1G download.
>> >> Is this a head end provisioning problem or related to Docsis 3.0 (or
>> >> later) modems?
>> > For DOCSIS the issue seems to be an unfortunate frequency split between up and downstream and use of lower efficiency coding schemes .
>> > Over here the incumbent cable isp provisions  fifty Mbps for upstream and plans to increase that to hundred once the upstream is switched to docsis 3.1.
>> > I believe one issue is that since most of the upstream is required for the reverse ACK traffic for the download and hence it can not be oversubscribed too much.... but I think we have real docsis experts on the list, so I will stop my speculation here...
>> >
>> > Regards
>> >           Sebastian
>> >
>> >
>> >
>> >
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