[Cake] Stranger target behaviour

Sebastian Moeller moeller0 at gmx.de
Sun Nov 1 11:05:45 EST 2015

Dear friends of cake,

On Nov 1, 2015, at 14:21 , Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> wrote:

> On 01/11/15 09:47, Sebastian Moeller wrote:
>> Hi there,
>> On Oct 31, 2015, at 21:29 , Dave Taht <dave.taht at gmail.com> wrote:
>>> The second one is from the interval >> 4, which equates to 6.2ms. I
>>> note I picked that because some early data (2012) we had showed that
>>> target slightly greater than cable media acquision (6ms) time was a
>>> slight win, and it did not hurt to use a number more evenly divisible
>>> in binary than the arbitrary 5%.
>> 	Well, but should it not be 6.2ms even if no rtt is explicitly requested? Currently cake has a lot of corner-cases that are not too well documented either.
> Sebastian as ever picks up on the exact source of my confusion/point.
> If 'target=interval/16' is the new mantra then the defaults built in to
> cake qdisc should be changed, otherwise we have the current situation
> which is:  Default Interval=100ms, target=5ms.  If I specify rtt 100ms
> via the joys of tc, then I have: Interval=100ms, target=6.2ms.  If I
> specify a target keyword such as 'internet' which also has an interval=
> 100ms, then target become 5ms again.  Somewhat inconsistent.

	I believe I just fixed this by initializing target in sch_cake to "interval >> 4”, I opted for the calculation instead of the simple number 6250 to sort of document the pattern and tried to put in a comment explaining why this is okay with codel's theory. Please note, I did not really test this, so for all I know it might break spectacularly...
	Slightly different question, I have a few cosmetic changes for tc, so which repository to commit this too, is tc-adv to be the gathering point for changes to be considered?

Best Regards

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