On 22 Mar 2024, at 19:58, Ashish Varma via discuss wrote:
> Hi
> I have been trying to look at the concept of recirculation in OVS.
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> Found an old description by Joe Stringer:
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> *OVS_ACTION_ATTR_RECIRCULATE:* Open vSwitch datapath interface extension.
> Not exposed at the OpenFlowlayer.* Datapath interface inserts this action
> when it needs more informationabout the packet, part way through rule
> processing.* Commits all packet modifications and tells the datapath to
> re-insert thepacket with an ID (skb_mark) attached.* Re-inserted packets go
> through the standard parse/lookup/upcall procedure* Upcall uses the
> skb_mark to continue rule processing where therecirculate happened* This
> allows the datapath to re-parse a packet and provide moreinformation part
> way through rule-processingThe goal of in-kernel recirculation is to allow
> the kernel to do morethan one flow lookup for a single packet. The initial
> use case is forMPLS support. I don't know the details.*
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> What are the current scenarios in which a re-circulation happens in the
> datapath?
> Would appreciate an exhaustive list if possible?
> I believe sending the packet to conntrack for lookup / commit would cause a
> recirc?
Hi Ashish,
As you've previously noted, there could be numerous reasons for this
occurrence. Fortunately, all the translation occurs within a single file,
namely ofproto/ofproto-dpif-xlate.c. In fact, the following provides some
explanation as to why this is happening:
https://github.com/openvswitch/ovs/blob/c6538b443984e10c266d7e75e797ef2f1b722d61/ofproto/ofproto-dpif-xlate.c#L285
You could examine all freeze/unfreeze occurences, as well as factors such as
conntrack and cloning. While not exhaustive, some potential causes for
recirculation include conntrack, packet modifications, packet cloning, MPLS,
and bonding. Alternatively, you could search for instances where
OVS_ACTION_ATTR_RECIRC is added and work backward from there.
Hope this will get you going.
//Eelco
> Thanks,
> Ashish.
>
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