Re: [kvm-devel] [PATCH/RFC 0/2] CPU hotplug virtio driver

Glauber de Oliveira Costa wrote:

I'm sending a first draft of my proposed cpu hotplug driver for kvm/virtio
The first patch is the kernel module, while the second, the userspace pci device.

The host boots with the maximum cpus it should ever use, through the -smp parameter.
Due to real machine constraints (which qemu copies), i386 does not allow for any addition
of cpus after boot, so this is the most general way.

I do however, include an "attempt_buffer" in the userspace part. It's purpose is to
allow tools like virt-manager to set a max_cpus (-smp), and a desired number of cpus
in their configuration files. (and AFAICT, there's is no easy way for them to tell when the
backend driver is up and running)

Other than that, it should be pretty much straightforward.

Looking forward for your comments

  

I would much prefer to see cpu hotplug implemented via acpi.  Such an 
implementation would work on older kernels without change, and will also 
work with other operating systems.  It isn't a high-speed interface so 
virtio doesn't buy us anything.

Linux appears to support it (CONFIG_ACPI_HOTPLUG_CPU) so all that's 
needed is the host side support (likely qemu/bios only).  Of course 
hacking on acpi is fun, if you're the kind of person than enjoys dental 
surgery.

-- 
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