Re: [Codel] [PATCH v5] pkt_sched: codel: Controlled Delay AQM

[dave taht <dave.taht@gmail.com>]

On 05/05/2012 04:07 PM, Eric Dumazet wrote:
> On Sat, 2012-05-05 at 15:48 -0700, dave taht wrote:
>
>> Stalking butterflies. (
>> http://en.wikipedia.org/wiki/File:Lorenz_attractor_yb.svg )
>>
>> I suspected also we would have issues as we hit some natural quantums
>> (clock rate/interrupt rate/bql estimator etc) but for all I know it's
>> just a plain bug. I need a reboot. Goin to dinner.
>>
> This part of Codel seems suspicious (last page )
>
> // If min went above target close to when we last went below it
> // assume that the drop rate that controlled the queue on the
> // last cycle is a good starting point to control it now.
> if (now - drop_next<  16.*interval) {
> 	int c = count - 1;
> 	count = c<1? 1 : c;
> else {
> 	count = 1;
> }
>
>
> I suggest to replace it by a more conservative algo :
>
> // If min went above target close to when we last went below it
> // assume that sqrt(half) the drop rate that controlled the queue on the
> // last cycle is a good starting point to control it now.
> if (now - drop_next<  16.*interval) {
> 	int c = count>>  1;
> 	count = c<1? 1 : c;
> else {
> 	count = 1;
> }
>
I don't buy it. See previous mail.

count - some_x sure.

> With this change, my q->count max value is 12000
>
>
>