Re: [Xen-devel] How does the Xen kernel change the vcpu number of a domain?

[Bei Guan <gbtju85@xxxxxxxxx>]

2014-06-13 16:59 GMT+08:00 Wei Liu <wei.liu2@xxxxxxxxxx>:

On Fri, Jun 13, 2014 at 03:19:08PM +0800, Bei Guan wrote:
> Hi All,
>
> I try to figure out that how the command "xl vcpu-set" works. I find out
> that the command "xl vcpu-set" calls the method
> libxl__set_vcpuonline_xenstore() to set the state of the vcpu in the
> Xenstore path /local/domain_id/cpu/vcpu_id/availability. The value of the
> key "availability" is set to "online" while the the vcpu number will
> increase. When the key is set to "offline" the vcpu number will decrease.
>
> What I want to know is how does the vcpu number increase/decrease according
> to the vcpu state in the Xenstore? ÂHow can I find the method that really
> does the work?
>

Linux kernel code drivers/xen/cpu_hotplug.c. It sets up a xenstore watch
for "cpu" xenstore node and handles event accordingly.

Thank you very much for your reply.

I'm using Xen-4.1.2. I also find that the Xen code tools/ioemu-qemu-xen/xenstore.c sets a Xenstore watch for /loca/domain/domid/cpu. It handles the watch event in the method xenstore_procees_vcpu_set_event(char **vec). So, what's difference between the two Xenstore watch in the Linux kernel and qemu-xen? Is the Xenstore watch in qemu-xen for HVM domains that are without PV drivers?

Thank you very much.

Â

Wei.

> Any reply is appreciated. Thank you all very much.
>
> --
> Best Regards,
> Bei Guan

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--
Best Regards,

Bei Guan

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