[Bloat] [Cerowrt-devel] beating the drum for BQL

Mikael Abrahamsson swmike at swm.pp.se
Thu Aug 23 11:32:26 EDT 2018

On Thu, 23 Aug 2018, Sebastian Moeller wrote:

> router should be able to handle at least the sold plan's bandwidth with 
> its main CPU...)

There is exactly one SoC on the market that does this, and that's Marvell 
Armada 385, and it hasn't been very successful when it comes to ending up 
in these kinds of devices. It's mostly ended up in NASes and devices such 
as WRT1200AC, WRT1900ACS, WRT3200AC.

> 	Sure doing less/ a half asses job is less costly than doing it 
> right, but in the extreme not doing the job at all saves even more 
> energy ;). And I am not sure we are barking up the right tree here, it 
> is not that all home CPE are rigorously optimized for low power and 
> energy saving... my gut feeling is that the only optimizing principle is 
> cost for the manufacturer/OEM and that causes underpowered CPU that are 
> packet-accerlerated"-doped to appear to be able to do their job. I might 
> be wrong though, as I have ISP internal numbers on this issue.

The CPU power and RAM/flash has crept up a lot in the past 5 years because 
other requirements in having the HGW support other applications than just 
being a very simple NAT44+wifi router.

Cost is definitely an optimization, and when you're expected to have a 
price-to-customer including software in the 20-40 EUR/device range, then 
the SoC can't cost much. There has also been a lot of vendor lock-in.

But now speeds are creeping up even more, we're now seeing 2.5GE and 10GE 
platforms, which require substantial CPU power to do forwarding. The Linux 
kernel is now becoming the bottleneck in the forwarding, not even on a 
3GHz Intel CPU is it possible to forward even 10GE using the normal Linux 
kernel path (my guess right now is that this is due to context switching 
etc, not really CPU performance).

Marvell has been the only one to really aim for lots of CPU performance in 
their SoC, there might be others now going the same path but it's also a 
downside if the CPU becomes bogged down with packet forwarding when it's 
also expected to perform other tasks on behalf of the user (and ISP).

Mikael Abrahamsson    email: swmike at swm.pp.se

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