[pve-devel] [PATCH v8 0/8] Add basics for custom CPU models

Eneko Lacunza elacunza at binovo.es
Thu Feb 13 16:22:43 CET 2020


Hi again,

It is also documented elsewhere:
https://www.linux-kvm.org/page/Migration#Note

Cheers

El 13/2/20 a las 16:12, Eneko Lacunza escribió:
> Hi Stefan,
>
> El 13/2/20 a las 15:58, Stefan Reiter escribió:
>> Hi,
>>
>> On 2/13/20 1:27 PM, Eneko Lacunza wrote:
>>> Hi Stefan,
>>>
>>> Do you think this could help specifying a custom CPU model that will 
>>> migrate VMs with more than 1 core between Intel and AMD CPUs?
>>> https://bugzilla.proxmox.com/show_bug.cgi?id=1660
>>>
>>
>> as discussed on the bug report you linked, live migration between 
>> hosts using different vendors' CPUs is very much unsupported in 
>> general (with KVM-enabled VMs). Even if it _appears_ to work, there 
>> are no guarantees about stability.
>>
>> That said, if you find a specific CPU flag configuration that seems 
>> to work for you (like comment #12 in the report mentions), this 
>> series would indeed allow you to specify it as a custom CPU model 
>> instead of having to use the '-args' parameter.
> I don't understand why you insist that this isn't supported. Linux KVM 
> FAQ says otherwise:
>
> https://www.linux-kvm.org/page/FAQ#Does_KVM_support_live_migration_from_an_AMD_host_to_an_Intel_host_and_back.3F 
>
>
> "
> Does KVM support live migration from an AMD host to an Intel host and 
> back?
>
> Yes. [...]
> "
>
> I understand that there can be bugs, or maybe Proxmox VE as a product 
> can decide no to support such a feature; but technically upstrean says 
> that it should work. Shall I report the issue upstream directly?
>
> Thanks a lot
> Eneko
>>
>> Hope that helps,
>>
>> Stefan
>>
>>> Thanks a lot
>>> Eneko
>>>
>>>
>>> El 12/2/20 a las 16:11, Stefan Reiter escribió:
>>>> Based on the RFC and following on- and off-list discussion about 
>>>> custom CPU
>>>> models [0].
>>>>
>>>> In essence, this revised patch allows a user to specify custom CPU 
>>>> models in
>>>> /etc/pve/cpu-models.conf (section-config style [1]), where VMs 
>>>> using that CPU
>>>> model inherit details from the definition. This removes any fragile
>>>> "auto-magical" CPU flag detection, while still giving the user a 
>>>> way to create
>>>> VMs with the best possible subset of CPU features maintaining 
>>>> live-migration
>>>> compatibility.
>>>>
>>>> Includes the infrastructure for broadcasting supported CPU flags 
>>>> for each
>>>> cluster-node via the key-value store - this is not necessary for the
>>>> custom-cpu feature in particular, but I think could prove useful for
>>>> implementing the GUI part (e.g. show the user which flags are 
>>>> supported on which
>>>> nodes).
>>>>
>>>>
>>>> v7 -> v8:
>>>> * rebase on master, fix tests now using +pve0
>>>> * fixed nits noted by Thomas
>>>> * moved live-migration/snapshot patches forward to avoid temporary 
>>>> breakage
>>>> * fix CPU hotplug with custom CPUs
>>>> * guard mkdir with check_cfs_is_mounted and also run before write
>>>> * fix rebase-error in cfg2cmd tests (getaddrinfo_all)
>>>> * dropped applied patches
>>>>
>>>> I deliberately didn't add any version_guard checks, since I don't 
>>>> think a bump
>>>> is the right thing to do here (I say, after I waited for the 
>>>> pve-version series
>>>> to be applied for making this v8).
>>>>
>>>> Doing so would break custom CPUs on older machine versions (since 
>>>> I'd have to
>>>> pin it to 4.1~pve2) for no reason. The idea would have been to show 
>>>> a neat error
>>>> message, but since up to this point we didn't even check the 
>>>> pve-version on
>>>> migration, it wouldn't help much. Besides, migration to older 
>>>> versions already
>>>> fails cleanly with a semi-readable message ('Unknown option: 
>>>> force-cpu').
>>>>
>>>>
>>>> < see [2] for older history >
>>>>
>>>>
>>>> [0]: https://pve.proxmox.com/pipermail/pve-devel/2019-July/038268.html
>>>> [1]: e.g.:
>>>> cpu-model: custom-cpu-name
>>>>      host-phys-bits 1
>>>>      flags +aes;+avx;+avx2
>>>>      reported-model kvm64
>>>> [2] 
>>>> https://pve.proxmox.com/pipermail/pve-devel/2020-January/041278.html
>>>>
>>>>
>>>> qemu-server: Stefan Reiter (8):
>>>>    Adapt CPUConfig to handle custom models
>>>>    Verify VM-specific CPU configs seperately
>>>>    Include "-cpu" parameter with live-migration
>>>>    Include "-cpu" parameter with snapshots/suspend
>>>>    Add helpers to better structure CPU option handling
>>>>    Rework get_cpu_options and allow custom CPU models
>>>>    fix #2318: allow phys-bits and host-phys-bits CPU settings
>>>>    cfg2cmd: add test cases for custom CPU models
>>>>
>>>>   PVE/API2/Qemu.pm                              |  10 +-
>>>>   PVE/QemuConfig.pm                             |  36 +-
>>>>   PVE/QemuMigrate.pm                            |  22 +
>>>>   PVE/QemuServer.pm                             |  44 +-
>>>>   PVE/QemuServer/CPUConfig.pm                   | 477 
>>>> +++++++++++++++---
>>>>   test/cfg2cmd/custom-cpu-model-defaults.conf   |   8 +
>>>>   .../custom-cpu-model-defaults.conf.cmd        |  24 +
>>>>   test/cfg2cmd/custom-cpu-model.conf            |   8 +
>>>>   test/cfg2cmd/custom-cpu-model.conf.cmd        |  27 +
>>>>   test/cfg2cmd/i440fx-win10-hostpci.conf.cmd    |   2 +-
>>>>   test/cfg2cmd/minimal-defaults.conf.cmd        |   2 +-
>>>>   test/cfg2cmd/pinned-version.conf.cmd          |   2 +-
>>>>   .../q35-linux-hostpci-multifunction.conf.cmd  |   2 +-
>>>>   test/cfg2cmd/q35-linux-hostpci.conf.cmd       |   2 +-
>>>>   test/cfg2cmd/q35-win10-hostpci.conf.cmd       |   2 +-
>>>>   test/cfg2cmd/simple1.conf.cmd                 |   2 +-
>>>>   test/cfg2cmd/spice-enhancments.conf.cmd       |   2 +-
>>>>   test/cfg2cmd/spice-linux-4.1.conf.cmd         |   2 +-
>>>>   test/cfg2cmd/spice-usb3.conf.cmd              |   2 +-
>>>>   test/cfg2cmd/spice-win.conf.cmd               |   2 +-
>>>>   test/run_config2command_tests.pl              |  23 +
>>>>   21 files changed, 609 insertions(+), 92 deletions(-)
>>>>   create mode 100644 test/cfg2cmd/custom-cpu-model-defaults.conf
>>>>   create mode 100644 test/cfg2cmd/custom-cpu-model-defaults.conf.cmd
>>>>   create mode 100644 test/cfg2cmd/custom-cpu-model.conf
>>>>   create mode 100644 test/cfg2cmd/custom-cpu-model.conf.cmd
>>>>
>>>
>>>
>>
>
>


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