Re: [Cake] Cake over satellite

[Sebastian Moeller <moeller0@gmx.de>]

Hi Kevin,



On Oct 20, 2015, at 19:32 , Kevin Darbyshire-Bryant <kevin@darbyshire-bryant.me.uk> wrote:

> On 19/10/15 20:05, Sebastian Moeller wrote:
>> Hi,
>> 
>> On October 19, 2015 10:24:01 AM CDT, Dave Taht <dave.taht@gmail.com> wrote:
>>> well, yes, but we can do it in the lab *this week*, before he takes
>>> the dingos on....
>> Good idea, als I am at A conference right now and will not find the time to make the changes to TC in time. I believe that cake should certainly A) set A reasonable target by default and B) still allow the user to explicitly request something else. Currently, I believe cake does only A)...
>> 
>> Besteht Regards
>>        Sebadtian
>> 
>> 
> 
> As an FYI:
> 
> 
> tc has a number of calculations for interval & target
> 
> If an rtt is specified then target is 5% of interval with 1uS
> (microsecond!) and 5mS (millisecond) lower & upper bounds.
> 
> The keyword predefined rtt values are:
> 
> datacentre (100uS), lan (1mS), metro(10mS), regional(30mS),
> internet(100mS), oceanic(300mS), satellite(1000mS), interplanetary(1hour!)
> Corresponding targets are 5uS, 50uS, 500uS, 1.5mS and everything from
> internet onwards as a 5mS target.
> 
> Although these are the values passed into cake from tc, that isn't the
> final story with regard to calculations as cake qdisc has some further
> sanity checks.
> 
> If a link bandwidth is specified then the target is set to the max of
> '1.5 MTU's worth of link time' and the target value passed by tc.  The
> interval is set to max of '8 times the calculated target' and interval
> value passed by tc.
> 
> So whilst tc supplies an rtt/interval and a 5% calculated target, cake
> itself will override this with sensible values if that makes sense for a
> 'slow' link.

	Thanks for elucidating this. I believe that cake should honor silly requests by the user as long as those were stated explicitly by the users and are possible (so target <= interval). It is great that cake has sane defaults and I also believe it would be helpful if cake noticed the user of unusual parameter configuration, but in the end the user should be able to control the parameters. (I am fine with having a —override_sane_cake_defaults command line switch to make it hard to do silly things accidentally). “Do the right thing by default, but allow unreasonable configurations if asked nicely” should be the goal here, I believe (but I admit Jonathan’s project, and hence his call)

Best Regards
	Sebastian


> 
> Kevin
> 
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