Summary: OvS last commit 52f793b I am trying to modify the switch's code to use a round robin scheduler for sending asynchronous messages (especially PACKET_IN messages) to one of the controllers within a multiple controller SDN setup. After traversing the code I think I found where I need to insert this round robin scheduler, line 4766 and 6225 of ofproto-dpif-xlate.c.
I plan on modifying this part of the code and testing it to see if I was correct but it would be great to have some feedback from the community on this. 1) Am I on the right path, do I only need to modify the code around line 4766? Or do I need to modify another part of the code? 2) What is OFPACT_CONTROLLER case for? From what I can gather macro OFPACT_FOR_EACH uses a macro that goes through a list that deal with table entry actions but it could call the execute_controller_action() function and I don't know why it would. 3) What does emit_continuation() function do? It looked like it had to do with table lookups instead of sending asynchronous messages to the controller. If it only does table lookups why would it call the execute_controller_action() function. Details: I setup a simple Mininet topology with a single switch, 3 user computers, and 2 controllers, where everything is connected to the switch. Currently when the switch receives a packet with no corresponding forwarding rule it sends a request to both controllers. I would like it so that it sends the forwarding rule request in a round robin method. So the first forwarding rule request will be sent to only controller 1, then the next forwarding rule request will be sent to only controller 2, then the next one to only controller 1, then the next one only to controller 2, etc. Along side other documents I've read a description of the Open vSwitch architecture (https://www.slideshare.net/rajdeep/openvswitch-deep-dive) and pages 25-28 of Pavel's master thesis (https://mail.openvswitch.org/ pipermail/ovs-discuss/2017-February/043763.html) to get a better understanding of the internals of OvS. This information paired with the following post (https://mail.openvswitch.org/pipermail/ovs-discuss/2016- March/040236.html) informed me that the source code I am looking for is used within the Userspace and located within the ofproto directory. I started looking in the ofproto directory for the handle_openflow() function. This eventually lead me to look at the structure and usage of ofconn which lead me to line 1741 of connmgr.c where I found the structure ofproto_async_msg and function connmgr_send_async_msg. After following the function I noticed that ofproto_async_msg.controller_id is assigned in only 2 different places; within the execute_controller_action() and emit_continuation() functions. I continued following the execute_controller_action() function and noticed that it's called in only 5 different locations all within the file ofproto-dpif-xlate.c. Within those 5 locations only lines 4766 and 6225 use some sort of loop to craft and send asynchronous messages to multiple controllers. So my questions become: 1) Am I on the right path, do I only need to modify the code around line 4766? Or do I need to modify another part of the code? 2) What is OFPACT_CONTROLLER case for? From what I can gather macro OFPACT_FOR_EACH uses a macro that goes through a list that deal with table entry actions but it could call the execute_controller_action() function and I don't know why it would. 3) What does emit_continuation() function do? It looked like it had to do with table lookups instead of sending asynchronous messages to the controller. If it only does table lookups why would it call the execute_controller_action() function.
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