Note: This bug is displayed in read-only format because
the product is no longer active in Red Hat Bugzilla.
RHEL Engineering is moving the tracking of its product development work on RHEL 6 through RHEL 9 to Red Hat Jira (issues.redhat.com). If you're a Red Hat customer, please continue to file support cases via the Red Hat customer portal. If you're not, please head to the "RHEL project" in Red Hat Jira and file new tickets here. Individual Bugzilla bugs in the statuses "NEW", "ASSIGNED", and "POST" are being migrated throughout September 2023. Bugs of Red Hat partners with an assigned Engineering Partner Manager (EPM) are migrated in late September as per pre-agreed dates. Bugs against components "kernel", "kernel-rt", and "kpatch" are only migrated if still in "NEW" or "ASSIGNED". If you cannot log in to RH Jira, please consult article #7032570. That failing, please send an e-mail to the RH Jira admins at rh-issues@redhat.com to troubleshoot your issue as a user management inquiry. The email creates a ServiceNow ticket with Red Hat. Individual Bugzilla bugs that are migrated will be moved to status "CLOSED", resolution "MIGRATED", and set with "MigratedToJIRA" in "Keywords". The link to the successor Jira issue will be found under "Links", have a little "two-footprint" icon next to it, and direct you to the "RHEL project" in Red Hat Jira (issue links are of type "https://issues.redhat.com/browse/RHEL-XXXX", where "X" is a digit). This same link will be available in a blue banner at the top of the page informing you that that bug has been migrated.
DescriptionEduardo Habkost
2012-06-18 17:41:13 UTC
We need to implement this on 6.4, too.
+++ This bug was initially created as a clone of Bug #824991 +++
Sometimes we want to update an existing QEMU CPU model, because of a new feature, or because a bug needs to be fixed. But existing virtual machines using the CPU model can't change under the guest's feet when live-migrated. To make this work, we need to implement:
- Versioned CPU models, so new CPU models can get the fixes or new features while the existing CPU models keep the same.
- Per-machine-type CPU model aliases, so users can get the latest version of a CPU model automatically, but keep the same CPU when live-migrating to a newer QEMU version.
So, the current plan is:
- Make per-machine-type CPU model changes, but only essential and minimal ones, not visible to libvirt (such as the bugs caused by wrong "level" field)
- The only exception for the "minimal and not visible to libvirt" rule will be TSC-deadline. libvirt will require TSC-deadline support on the host even for "-M rhel6.3.0 -cpu SandyBridge"
- The QEMU<=>libvirt API for CPU model and feature probing won't be implemented in 6.4.
just to make sure i understand correctly:
On a 6.3 host
-cpu SandyBridge with -M rhel6.3.0 does not have TSC
on a 6.4 host
-cpu SandyBrdige with -M rhel6.3.0 does not have TSC[1]
-cpu SandyBridge with -M rhel6.4.0 does have TSC
[1] libvirt will require the host to have it, but it will not be exposed to the guest, so live migration to a rhel 6.3 host will work.
(In reply to comment #8)
> just to make sure i understand correctly:
> On a 6.3 host
> -cpu SandyBridge with -M rhel6.3.0 does not have TSC
>
> on a 6.4 host
> -cpu SandyBrdige with -M rhel6.3.0 does not have TSC[1]
> -cpu SandyBridge with -M rhel6.4.0 does have TSC
>
>
> [1] libvirt will require the host to have it, but it will not be exposed to
> the guest, so live migration to a rhel 6.3 host will work.
That's correct.
(But, please, don't call the feature just "TSC", it's called "TSC deadline", or "TSC deadline timer")
Reproduction on qemu-kvm-0.12.1.2-2.316.el6:
1. Boot a guest with "-M rhel6.4.0 -cpu SandyBridge" on a SandyBridge host.
2. Check cpuinfo after guest boot up.
Result: There's no "tsc_deadline_timer" flag inside guest.
========================
Verification on qemu-kvm-0.12.1.2-2.320.el6:
1. Boot a guest with "-M rhel6.4.0 -cpu SandyBridge" on a SandyBridge host and check cpuinfo after guest boot up.
==> There's "tsc_deadline_timer" flag inside guest.
2. Boot a guest with "-M rhel6.3.0 -cpu SandyBridge" on a SandyBridge RHEL6.4 host and check cpuinfo after guest boot up.
==> There's no "tsc_deadline_timer" flag inside guest.
3. Ping-pong migration beween two RHEL6.4 host with "-M rhel6.4.0 -cpu SandyBridge".
==> Migration finished successfully. Guest cpu flag keeps the same before and after migration (have "tsc_deadline_timer" flag). No time drift inside guest after migration.
4. Ping-pong migration between RHEL6.3 and RHEL6.4 host with "-M rhel6.3.0 -cpu SandyBridge". (Both hosts are SandyBridge)
==> Migration finished successfully. Guest cpu flag keeps the same before and after migration (have NO "tsc_deadline_timer" flag). No time drift inside guest after migration.
So, this bug is verified pass.
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory, and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
http://rhn.redhat.com/errata/RHBA-2013-0527.html