[ovs-discuss] packet buffering on OVS

[Yikai Lin]

Hi All,

As we all know, OVS(and practically most OF switches) can be configured to buffer missed packets and to send only the headers to the controller as packet-in messages(containing the buffer_id). 

From previous discussions(https://www.mail-archive.com/discuss@openvswitch.org/msg16624.html <https://www.mail-archive.com/discuss@openvswitch.org/msg16624.html>), I learnt that the buffer size for each flow is 256 (in # of packets). Another thread(http://openvswitch.org/pipermail/discuss/2013-October/011580.html <http://openvswitch.org/pipermail/discuss/2013-October/011580.html>) pointed to the actual implementation of the buffering, but that wasn’t in the latest build of OVS anymore(i.e., 2.6). 

So my questions will be:

1. What is the latest implementation regarding the packet buffering behavior in OVS?

2. If the buffer is allocated per “flow”, what is the definition of flow here, five-tuple?

3. Where are some of the key files that I might find useful if I want to, for example, tweak the buffer size?

4. What is the design principle behind this size? Why can’t it be larger or smaller?

5. Is it still true that, for multiple missed packets buffered on switch(which generate multiple packet-ins), the controller has to send out the same amount of packet-outs to properly deal with these packets? Or, can the controller send out one packet-out(or flow-mod), and it instructs the switch to process other packets of the same flow that are buffered on switch?

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I know I have asked a couple questions, but any information or insight regarding any of the questions will be very much welcomed. Thanks.

Best,
Yikai
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