Question on CPU masking with qemu and xen
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Hello all
I have a question but dot know enough about Xen hypervisor to answer it.
So it simple why cant XCP-ng mask the type of CPU that the vms running on.
Take for example the KVM on proxmox you can set host pass-through to send all CPU functions to the vm or mask it to an intel Xeon scalable or AMD Epyc.
I see that host pass-through is what XCP-ng does but was wondering why.Doesnt masking the cpu make the vm more portable as the profile can be set to for example QEMU-xen or something making it possible to say migrate a vm live from AMD to intel n different pools or a heterogeneous cluster.
And one last thing if it is possible is there no way to emulate other architecture supported by qemu such as arm64 or does xen hypervisor still need more features built out on arm before that i possible. Asking because my use case is i cant afford a raspberry pi but have alot of compute on x86 why not emulate arm 64 on the hypervisor rather than in a vm
Just asking would appreciate a response. thanks
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@brodiecyber said in Question on CPU masking with qemu and xen:
Hello all
I have a question but dot know enough about Xen hypervisor to answer it.
So it simple why cant XCP-ng mask the type of CPU that the vms running on.
Take for example the KVM on proxmox you can set host pass-through to send all CPU functions to the vm or mask it to an intel Xeon scalable or AMD Epyc.
I see that host pass-through is what XCP-ng does but was wondering why.It doesn't exactly work this way.
With XCP-ng, it works at pool level, it basically takes the lowest CPU feature level of your hosts of the pool, and sets all VM to use it. That way you should always be able to migrate to another machine of the same pool, while not having to manually set the feature levels to improve performance.Doesnt masking the cpu make the vm more portable as the profile can be set to for example QEMU-xen or something making it possible to say migrate a vm live from AMD to intel n different pools or a heterogeneous cluster.
In practice, you can't reliably live migrate between Intel and AMD architecture (even with QEMU) due to various subtle architecture differences. It may somewhat work with luck if the guest is using a ancient processing model (like 32-bits) but that's not really something we support.
And one last thing if it is possible is there no way to emulate other architecture supported by qemu such as arm64 or does xen hypervisor still need more features built out on arm before that i possible. Asking because my use case is i cant afford a raspberry pi but have alot of compute on x86 why not emulate arm 64 on the hypervisor rather than in a vm
Emulating a completely different CPU architecture while technically possible, is a completely different story.
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For migration between vendors (AMD/Intel) I suggest the warm migration feature of XOA, solving the problem with only few minutes of interruption.
