[ovs-dev] [PATCH v3 3/3] OVN: Add ovn-northd IGMP support

Ben Pfaff blp at ovn.org
Fri Jul 12 17:34:32 UTC 2019

On Thu, Jul 11, 2019 at 05:20:58PM +0200, Dumitru Ceara wrote:
> While doing some scale testing I realized that walking the rows of the
> IGMP_Group table in ovn-northd in the order we get them from the
> database might create an issue: ovn_igmp_group_add will create a new
> multicast_group for every unique IGMP group address and allocate a
> tunnel-id for it. However, because rows are not processed in the order
> they were added to the database, it can happen that multicast groups
> that didn't actually change will get a different tunnel-id triggering
> a change in the associated logical flows.

Ouch.  Let's avoid that problem!

> 2. Maintain a cache (hashtable) of allocated multicast group
> tunnel-ids between subsequent  runs of the ovn-northd loop:
> - Once all IGMP_Group entries are processed and their corresponding
> Multicast_Group entries are collected we'd need to store a mapping
> (per datapath) between IGMP group address and multicast group
> tunnel-id.
> - Next time ovn-northd walks the IGMP_Group table, before allocating a
> new tunnel-id for a multicast group entry it would check the "cache"
> from the previous run. If there's already an entry it would reuse the
> tunnel-id. If not, it will have to allocate a tunnel-id. Store the
> (IGMP group address, tunnel-id) mapping for next run.

This is the customary way, so it's what I recommend.

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