[Cake] Long-RTT broken again

[Sebastian Moeller]

Hi Jonathan,

On Nov 3, 2015, at 02:39 , Jonathan Morton <chromatix99 at gmail.com> wrote:

> 
>> On 2 Nov, 2015, at 20:29, Sebastian Moeller <moeller0 at gmx.de> wrote:
>> 
>> the initial commit was not as well tested as it should have been…
> 
> Indeed, and the obvious problems with it were why I reverted it.  I was able to put in a partial implementation by other means at the same time, but haven’t yet had time to polish off the rough edges.

	Well, I believe one of the next steps needs to be to expose limit to user-space, which would have Toke allowed his measurements and would have followed the example of most/all other leaf qdiscs and put policy into user space where it arguably belongs… if no one beats me to it I might go and try implement this, but behold it is not going to be pretty...

> 
> The question remains why a 15MB buffer (which comfortably exceeds the traditional FIFO rule of thumb for 1 second * 100Mbps) is apparently insufficient according to Toke’s tests, even with the target increased as requested.

	That also is a valid question that should be answered, but it would be great if cake had just enough knobs to allow working around this issue, to sort of compartmentalize different problem spheres and allow concurrent progress on different issues, no?

	Also what about the BUG_ON I managed to trigger during my testing? Could we just change this to a WARN_ON and “gracefully” fail the initialization of the qdisc with an appropriate message to the user? I am not sure that cake’s unhappiness should wedge a whole system...


Best Regards
	Sebastian

> 
> - Jonathan Morton
>