[Cake] Correct 'change' behaviour

[Sebastian Moeller]

Hi Toke,

me too ;)

On Nov 4, 2015, at 12:09 , Toke Høiland-Jørgensen <toke at toke.dk> wrote:

> Dave Taht <dave.taht at gmail.com> writes:
> 
>> in the general case, I recomend looking at the most current fq_codel
>> code to see how to do it as right as possible. There were several bugs
>> found and fixed in it as well....
> 
> Well, I did, and it doesn't seem to be doing anything different. So much
> so that I tried the same experiment on fq_codel:
> 
> $ sudo tc qdisc del dev eno1 root
> $ sudo tc qdisc replace dev eno1 root fq_codel target 100ms interval 200ms
> $ sudo tc qdisc replace dev eno1 root fq_codel target 5ms                 
> $ tc qdisc
> qdisc fq_codel 8007: dev eno1 root refcnt 2 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 200.0ms ecn 
> $ sudo tc qdisc del dev eno1 root                                         
> $ sudo tc qdisc replace dev eno1 root fq_codel target 5ms
> $ tc qdisc                                          
> qdisc fq_codel 8008: dev eno1 root refcnt 2 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms ecn 


$ sudo tc qdisc del dev eth0 root
$ sudo tc qdisc replace dev eth0 root fq_codel target 100ms interval 200ms
$ sudo tc qdisc replace dev eth0 root fq_codel target 5ms
$ sudo tc qdisc
qdisc fq_codel 800a: dev eth0 root refcnt 6 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 200.0ms ecn 
$ sudo tc qdisc del dev eth0 root
$ sudo tc qdisc replace dev eth0 root fq_codel target 5ms
$ sudo tc qdisc
qdisc fq_codel 800b: dev eth0 root refcnt 6 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms ecn 

$ uname -a
Linux happy-horse 3.16.7-24-desktop #1 SMP PREEMPT Mon Aug 3 14:37:06 UTC 2015 (ec183cc) x86_64 x86_64 x86_64 GNU/Linux



$ sudo tc qdisc del dev eth0 root
$ sudo tc qdisc replace dev eth0 root fq_codel target 100ms interval 200ms
$ sudo tc qdisc replace dev eth0 root fq_codel target 5ms
$ sudo tc qdisc
qdisc fq_codel 8003: dev eth0 root refcnt 6 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 200.0ms ecn 
$ sudo tc qdisc del dev eth0 root
$ sudo tc qdisc replace dev eth0 root fq_codel target 5ms
$ sudo tc qdisc
qdisc fq_codel 8004: dev eth0 root refcnt 6 limit 10240p flows 1024 quantum 1514 target 5.0ms interval 100.0ms ecn 
$ uname -a
Linux psychotb-01 3.19.0-31-generic #36~14.04.1-Ubuntu SMP Thu Oct 8 10:21:08 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
 
So at least the opensuse 3.16.7 and the ubuntu 3.19.0 kernels both suffer this issue. Maybe the kernel does this on purpose, or nobody ever tests this functionality…

Best Regards
	Sebastian


> 
> 
> I.e. fq_codel suffers from exactly the same problem.
> 
> Is this a bug or is it expected behaviour? I'd say bug?
> 
> -Toke
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