[LEDE-DEV] [PATCH v2] ramips: add support for Ubiquiti EdgeRouter X-SFP

[Kevin Darbyshire-Bryant]

On 12/06/17 21:00, Toke Høiland-Jørgensen wrote:
> p.wassi at gmx.at writes:
> 
>> My SQM configuration was basically just using cake + piece_of_cake.qos,
>> but that's clearly off topic for now. (I'm also CC'ing this mail to Toke,
>> the maintainer of sqm-scripts).
> 
> If you're crashing the box my guess would be there's a bug in the cake
> qdisc somewhere. What happens if you run SQM with fq_codel instead?
> 
> -Toke

This isn't the first time I've heard cake implicated in cpu stalls but 
trying to discern a signal in some of the noise is difficult.

Using 'fq_codel' would be a good first elimination round.

For 2nd round elimination:  Cake is the only qdisc to my knowledge that 
pulls apart large 'GSO' (Generic segmentation offload) packets prior to 
sending them up the stack, a process cake calls 'peeling'.  It does this 
to retain control on how to schedule a (up to 64K) 'super packet', 
breaking it up into a series of 1500 byte packets instead.  Some have 
reported 'messing with ethtool' to disable GSO as being helpful.  I know 
not how 'ethtool' works.

Whether this is a bug in the cake peeling code, network interface driver 
is unclear, and again anecdotal evidence suggests this is only seen on 
multi-cpu systems.  I dread to think what happens if one cpu starts 
'grabbing one of those large skbs' for sending purposes, whilst another 
(in cake) is busy breaking it apart, or indeed if that scenario is possible.

Some ideas/thoughts/things to try :-)  Apologies for the continuing hijack.

KDB