Priority and qid fields meaning

[MateusBragatto]

Hello there everyone!

I have some questions regarding the usage of multiqueue inside bmv2.

What are the meaning of both fields: qid and priority? Is there a link that I can read more about both?
For example: If i define priority = 1 and qid = 3 I'm giving the fourth qid the priority of 1? How does that work?

Thanks already!

[edgar-costa]

Hi,

Priority is used to set the packet priority at the ingress pipeline. That value is used by the Traffic manager to enqueue the packet.

The qid field is a read only field that gets the value of the queue ID it has been queued into. In this case, it will get the priority value you have used at the ingress. This information can be used at the egress for whatever you might need it.

You can see some info here: https://github.com/p4lang/behavioral-model/blob/main/docs/simple_switch.md

[MateusBragatto]

Thank you so much! Now it's very clear

Two more questions question that I have:

• In BMv2 the qids are distributed by ports, meaning each port can have a defined number of queues?
• In BMv2 is there a limit for registers readings? I'm creating a logic to read registers based on qid's infos.

[edgar-costa]

Hi @MateusBragatto,

Sorry for the long delay. I hope you found an answer to your questions.

• yes each port has its own qids
• there is no technically no register reading limit, however that is not the case on real hardware