can SFQ and perturb break paquet ordering ?

can SFQ and perturb break paquet ordering ?

[Julien Vehent]

Hi netdev folks,

I was digging into the sch_sfq code and I was wondering the following (I
assume it's nothing new, I'm just trying to get it right):

Let's consider one UDP connection that has two packets. Packet#1 goes to
bucket#1, then perturb modifies the hashing algorithms and thus Packet#2
goes to bucket#800.

If the round robin was positionned after bucket#1 but before bucket#800
when perturb occured, then Packet#2 will be sent before Packet#1. And since
UDP can't reordered, it will be processed before on the received end.

Am I getting this right or is there something in the code that I missed ?


Thanks for your help.

Julien Vehent

Re: can SFQ and perturb break paquet ordering ?

[Patrick McHardy]

Julien Vehent wrote:
> Hi netdev folks,
> 
> I was digging into the sch_sfq code and I was wondering the following (I
> assume it's nothing new, I'm just trying to get it right):
> 
> Let's consider one UDP connection that has two packets. Packet#1 goes to
> bucket#1, then perturb modifies the hashing algorithms and thus Packet#2
> goes to bucket#800.
> 
> If the round robin was positionned after bucket#1 but before bucket#800
> when perturb occured, then Packet#2 will be sent before Packet#1. And since
> UDP can't reordered, it will be processed before on the received end.
> 
> Am I getting this right or is there something in the code that I missed ?

That's correct.