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Bug 2318544 - Update docs explaining why and how to enable OVNEmitNeedToFrag for ml2/ovn tripleo config
Summary: Update docs explaining why and how to enable OVNEmitNeedToFrag for ml2/ovn tr...
Keywords:
Status: CLOSED MIGRATED
Alias: None
Product: Red Hat OpenStack
Classification: Red Hat
Component: documentation
Version: 17.1 (Wallaby)
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: z4
: 17.1
Assignee: James Smith
QA Contact: RHOS Documentation Team
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2024-10-14 14:16 UTC by Ihar Hrachyshka
Modified: 2025-01-11 20:11 UTC (History)
4 users (show)

Fixed In Version:
Doc Type: No Doc Update
Doc Text:
Clone Of:
Environment:
Last Closed: 2025-01-11 20:11:35 UTC
Target Upstream Version:
Embargoed:

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System ID Private Priority Status Summary Last Updated
Red Hat Issue Tracker OSP-32949 0 None None None 2024-10-14 14:17:12 UTC
Red Hat Issue Tracker OSP-33435 0 None None None 2025-01-11 20:11:38 UTC
Red Hat Issue Tracker   OSPRH-12953 0 None None None 2025-01-11 20:11:34 UTC

Description Ihar Hrachyshka 2024-10-14 14:16:43 UTC 
This bug was initially created as a copy of Bug #2314429

I am copying this bug because: 

We need to add a KCS explaining the failing scenario (MTU mismatch), how to deal with it (either fix mismatch or enable the flag in Tripleo templates). The KCS will apply to all z-releases for 17.x. We may later release async that would no longer require the KCS.

Since this behavior is currently different for ml2/ovs (emitting need frag packets) and ml2/ovn (not doing it by default), this should also be documented in migration guide for ovs->ovn for 17. Namely, suggesting that the flag for Tripleo should be set to True during migration.


Description of problem:

Enabling the "ovn_emit_need_to_frag" configuration option solves a gap between ML2/OVN and ML2/OVS but, it was left disabled by default because of a kernel requirement [0]. Now it seems that we could consider enabling this in the product for newer versions of OSP as the kernel requirements are no longer a problem.

I am opening this BZ as a request from a discussion had about a customer use-case on slack, see the internal discussion for more information: https://redhat-internal.slack.com/archives/C046JULBVJ7/p1727170946243269

[0] This feature requires kernel version >= 5.2 (upstream) before being enabled. One could run the following command to verify it before enabling in our product:

$ ovs-appctl -t ovs-vswitchd dpif/show-dp-features br-int

If the output contains: "Check pkt length action: Yes" means it is supported and can be enabled.

Enabling it on a non-supported kernel version will lead to critical performance degradation.

Version-Release number of selected component (if applicable):
17.1.3
Comment 8 Ihar Hrachyshka 2024-11-07 02:43:22 UTC 
Alex, thank you for the KCS. I removed RHOSO 18 from the list of platforms for the solution because it doesn't use TripleO and because the config flag is not available there. For RHOSO 18, configuration is done through CustomServiceConfig field of NeutronApi CR: https://github.com/openstack-k8s-operators/neutron-operator/blob/8108068a452f0d61a5854095f52a4f394f11b691/api/bases/neutron.openstack.org_neutronapis.yaml#L65

I think we should have a separate KCS for this (alternatively, a single KCS with two separate solutions described - you decide which is better). 

Thanks again.
Comment 9 Alex Stupnikov 2024-11-07 12:47:42 UTC 
Thank you Ihar. I have finalized KCS according to your guidelines.
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