a problem of preparing before cpu hot remove

a problem of preparing before cpu hot remove

[chenfan]

Hi All,

Recently, I'm implementing cpu hot-remove for QEMU. I has a question
that there is no chance for applications to prepare vcpu-hotremove
before cpu down. 
For example, if user specify cpu-pin for some applications, and its cpu
is removed, there is no notification to udev for preparing to do some
repin before cpu down. the applications would not change setting before
cpu down.

I want to know that whether there is a scenario that can notify the
applications for preparing before cpu down. and if preparing fails, I
want the cpu remove failure.

Thanks,
Chen

Re: a problem of preparing before cpu hot remove

[Greg KH]

On Wed, Jul 31, 2013 at 11:56:27AM +0800, chenfan wrote:
> Hi All,
> 
> Recently, I'm implementing cpu hot-remove for QEMU. I has a question
> that there is no chance for applications to prepare vcpu-hotremove
> before cpu down. 
> For example, if user specify cpu-pin for some applications, and its cpu
> is removed, there is no notification to udev for preparing to do some
> repin before cpu down. the applications would not change setting before
> cpu down.
> 
> I want to know that whether there is a scenario that can notify the
> applications for preparing before cpu down. and if preparing fails, I
> want the cpu remove failure.

Right now, there isn't one, but I suggest working with the kernel ACPI
developers as they are working on some kind of notification for this
thing for CPUs and memory, as memory has the same issue that CPUs do.

Hope this helps,

greg k-h