Mailing List Archive: Xen: Users

reboot needed to increase vcpus??

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geek at uniserve

Apr 19, 2012, 12:48 PM

Post #1 of 5 (180 views)
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reboot needed to increase vcpus??

In order to address a performance issue (or try to) I'd like to
allocate 4 vcpus to a domU. I think I need to increase that setting in
dom0's /etc/xen domU file. Is that correct? And do I need to reboot
either or both of dom0 and/or domU subsequently? and is there a
corresponding setting in domU?

Thanks. As you can see I'm new at this.

Dave

--
It is told that such are the aerodynamics and wing loading of the
bumblebee that, in principle, it cannot fly...if all this be
true...life among bumblebees must bear a remarkable resemblance to
life in the United States.

-- John Kenneth Galbraith, in American Capitalism: The Concept of
Countervailing Power

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sdj at rasmussenequipment

Apr 19, 2012, 1:36 PM

Post #2 of 5 (142 views)
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Re: reboot needed to increase vcpus?? [In reply to]

Dan,
From what I have seen, it depends on if you are using PV or HVM DomU's. PV
you can use the xm vcpu-set {domain} {#vcpus} and you should be good to go.
HVM you can use the same command but the Guest will have to be rebooted in
order to see the update.
If you are using a updated xen the command is xl I believe (I am on Debian
squeeze for my host so the commands above are what I use)

Shane

P.S. Sorry if this gets double posted.

On Thu, Apr 19, 2012 at 1:48 PM, Dave Stevens <geek [at] uniserve> wrote:

> In order to address a performance issue (or try to) I'd like to allocate 4
> vcpus to a domU. I think I need to increase that setting in dom0's /etc/xen
> domU file. Is that correct? And do I need to reboot either or both of dom0
> and/or domU subsequently? and is there a corresponding setting in domU?
>
> Thanks. As you can see I'm new at this.
>
> Dave
>
>
> --
> It is told that such are the aerodynamics and wing loading of the
> bumblebee that, in principle, it cannot fly...if all this be true...life
> among bumblebees must bear a remarkable resemblance to life in the United
> States.
>
> -- John Kenneth Galbraith, in American Capitalism: The Concept of
> Countervailing Power
>
>
>
> ______________________________**_________________
> Xen-users mailing list
> Xen-users [at] lists
> http://lists.xen.org/xen-users
>

--
Shane D. Johnson
IT Administrator
Rasmussen Equipment

admin at xenhive

Apr 19, 2012, 3:17 PM

Post #3 of 5 (141 views)
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Re: reboot needed to increase vcpus?? [In reply to]

You usually need to reboot the guest (domU) but not the dom0.

-----Original Message-----
From: xen-users-bounces [at] lists
[mailto:xen-users-bounces [at] lists] On Behalf Of Dave Stevens
Sent: Thursday, April 19, 2012 2:48 PM
To: xen-users [at] lists
Subject: [Xen-users] reboot needed to increase vcpus??

In order to address a performance issue (or try to) I'd like to
allocate 4 vcpus to a domU. I think I need to increase that setting in
dom0's /etc/xen domU file. Is that correct? And do I need to reboot
either or both of dom0 and/or domU subsequently? and is there a
corresponding setting in domU?

Thanks. As you can see I'm new at this.

Dave

--
It is told that such are the aerodynamics and wing loading of the
bumblebee that, in principle, it cannot fly...if all this be
true...life among bumblebees must bear a remarkable resemblance to
life in the United States.

-- John Kenneth Galbraith, in American Capitalism: The Concept of
Countervailing Power

_______________________________________________
Xen-users mailing list
Xen-users [at] lists
http://lists.xen.org/xen-users

_______________________________________________
Xen-users mailing list
Xen-users [at] lists
http://lists.xen.org/xen-users

james.harper at bendigoit

Apr 19, 2012, 8:19 PM

Post #4 of 5 (144 views)
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Re: reboot needed to increase vcpus?? [In reply to]

>
> In order to address a performance issue (or try to) I'd like to allocate 4 vcpus
> to a domU. I think I need to increase that setting in dom0's /etc/xen domU
> file. Is that correct? And do I need to reboot either or both of dom0 and/or
> domU subsequently? and is there a corresponding setting in domU?
>
> Thanks. As you can see I'm new at this.
>

If you change the config file then you probably need to shut down the VM then restart it. The config file isn't re-read on a reboot, for xm at least.

James

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Ian.Campbell at citrix

Apr 20, 2012, 3:24 AM

Post #5 of 5 (144 views)
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Re: reboot needed to increase vcpus?? [In reply to]

On Thu, 2012-04-19 at 21:36 +0100, Shane Johnson wrote:
> Dan,
> From what I have seen, it depends on if you are using PV or HVM
> DomU's. PV you can use the xm vcpu-set {domain} {#vcpus} and you
> should be good to go.

I'm not actually 100% sure but you might also need to configure the
guest (using "maxvcpus" and "vcpus") to have some spare "unplugged" CPU
slots at boot time such that you can dynamically increase them. e..g
vcpus = 2
maxvcpus = 8
would boot with 2 vcpus initially but give you space to increase this to
anything up to 8 (or down to 1).

> HVM you can use the same command but the Guest will have to be
> rebooted in order to see the update.

In HVM it depends a bit on the guest, if you do the maxvcpus thing then
you may well be able to plug more at run time and have them get picked
up.

AFAIK this all depends on the level of the guest kernel's support for
physical CPU hotplug and ACPI. For example with some you can hot plug
but not hotunplug a CPU.

> If you are using a updated xen the command is xl I believe (I am on
> Debian squeeze for my host so the commands above are what I use)

Correct.

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