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Bug 2138176 - [RFE] Postcopy Preemption (libvirt)
Summary: [RFE] Postcopy Preemption (libvirt)
Keywords:
Status: CLOSED MIGRATED
Alias: None
Product: Red Hat Enterprise Linux 9
Classification: Red Hat
Component: libvirt
Version: 9.3
Hardware: Unspecified
OS: Unspecified
unspecified
medium
Target Milestone: rc
: 9.3
Assignee: Jiri Denemark
QA Contact: Fangge Jin
URL:
Whiteboard:
Depends On: 2046606
Blocks:
TreeView+ depends on / blocked
 
Reported: 2022-10-27 13:49 UTC by Peter Xu
Modified: 2024-01-21 04:25 UTC (History)
12 users (show)

Fixed In Version:
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2023-09-22 13:14:29 UTC
Type: Story
Target Upstream Version:
Embargoed:

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System ID Private Priority Status Summary Last Updated
Red Hat Issue Tracker   RHEL-7100 0 None Migrated None 2023-09-22 13:14:24 UTC
Red Hat Issue Tracker RHELPLAN-137879 0 None None None 2022-10-31 10:04:38 UTC

Description Peter Xu 2022-10-27 13:49:40 UTC 
This bug is used to track libvirt support on postcopy preemption.

There's one new capability called "postcopy-preempt" supported for QEMU migration to speedup postcopy page request latencies.  To enable it, one can simply enable the capability before starting the migration for postcopy.  It does not need other special parameters.  The only limitation is it only works with protocol that supports multiple channels (similar to multi-fd in this case).
Comment 2 Jiri Denemark 2022-10-31 10:01:17 UTC 
Peter is there any downside of this feature or can we just enable it
automatically without an explicit request from a user? I guess we could
enabled it whenever postcopy and multi-fd are enabled...

And should it be enabled on both sides of migration or just one of them?
Comment 3 Peter Xu 2022-10-31 14:00:01 UTC 
(In reply to Jiri Denemark from comment #2)
> Peter is there any downside of this feature or can we just enable it
> automatically without an explicit request from a user? I guess we could
> enabled it whenever postcopy and multi-fd are enabled...

Postcopy and multifd are not yet compatible, afaict, so the new preempt mode is not compatible with multifd as well.  However yeah if any VM that can enable multifd should also be able to enable preempt when with postcopy, and it should always benefit postcopy, iiuc.

Currently one downside of preempt is we haven't gone though enough test, e.g., one known issue is multi channels can cause wrong ordered connections, similar to the multifd bug here:

https://bugzilla.redhat.com/show_bug.cgi?id=2137740

I'll need to further look into it, but hopefully shouldn't affect the long term plan of having it by default.

> 
> And should it be enabled on both sides of migration or just one of them?

Both sides.

Thanks!
Comment 7 Peter Xu 2023-06-30 16:47:25 UTC 
Jiri, any updates for this one?  Thanks,
Comment 8 RHEL Program Management 2023-09-22 13:12:09 UTC 
Issue migration from Bugzilla to Jira is in process at this time. This will be the last message in Jira copied from the Bugzilla bug.
Comment 9 RHEL Program Management 2023-09-22 13:14:29 UTC 
This BZ has been automatically migrated to the issues.redhat.com Red Hat Issue Tracker. All future work related to this report will be managed there.

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Comment 10 Red Hat Bugzilla 2024-01-21 04:25:30 UTC 
The needinfo request[s] on this closed bug have been removed as they have been unresolved for 120 days
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