Re: [PATCH 0/15] Review: acpi processor hotplug

[Avi Kivity <avi@qumranet.com>]

Glauber Costa wrote:
> Hi,
>
> In this series, I'm sending the result-so-far of my work
> with acpi for processor hotplug. I'm able to put a cpu up and down
> (with the help of some udev scripts I wrote), but it still has some
> known bugs and issues. For x86_64 linux machines (because the kernel
> supports it), you can plug cpus that _were not_ listed initially in 
> smp_cpus.
>
> The usage is : cpu_set x (online/offline), in qemu monitor.
> It will then send the proper signals to the cpu #x.
>
> However, it is important to note that:
>
> * there's no way to know if it suceeded. (ex, if the udev scripts are not
> running, the cpu will not be put up, and you'll never know)
> * there's no way to unconditionally send an add signal. (if you send BUS_CHECK again,
>   and the cpu is already marked as present, it will offline it instead)
>
> because of that, management gets a bit complicated. The ideal situation is to specify:
> "I want Y cpus", and have it. Error reported in case it fails. Because of that, I _still_
> advocate for an alternative virtio implementation. ACPI still plays its role in this scenario,
> but not the full role.
>
>   

Perhaps this can be implemented in userspace; I don't see anything that 
needs to be in the kernel for this.

Since it needs to work independently of networking, maybe it's a good 
first use for an AF_VIRT protocol family (which can be implemented on 
top of virtio).

> In my TODO list, you'll find:
> * fix some more issues in this code, and merge the gently comments I'm sure you'll make
>   

It's difficult with such near-perfect patchsets.  You're reducing me to 
whitespace comments.  Please post to qemu-devel as well so they can 
ignore it as usual.

> * device acpi hotplug
> * virtio cpu hotplug for linux (meaning refactoring the existing patch)
>   

Slightly related to this would be a qemu monitor mechanism to set 
vcpu->cpu affinity.

> * occupy 24 territories.
> * conquer 18 territories with at least 2 battalions on each. 
>   

Sounds risky.


-- 
error compiling committee.c: too many arguments to function


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