[Qemu-devel] windows guest virtio serial and balloon driver test issues

[Qemu-devel] windows guest virtio serial and balloon driver test issues

[Cao,Bing Bu]

Hi,

     Recently,I am testing windows guest driver on Win7 and WinXP(32bit) 
with the latest windows guest driver development source.
     Download from 
http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/


virtio-blk:
     It seems OK both on Win7 and WinXP,the r/w performance is better 
than IDE disk.



virtio-serial:
     I tried to test virtio serial driver using the test application in 
the project.

     WinXP:
     Write: OK
     Read: Error: Read File Failed.

     Win7:
     The test application return error "can not find vioserial device".
     But i debug the code and check that the GetDevicePath() return 
value is not NULL,and same as the value when testing on WinXP.
     Why the CreateFile() in init() not called? (:


virtio-balloon:

     QEMU monitor: device_add virtio-balloon-pci

     On the guest,a new device "PCI standard RAM controller" added.
     But the Device Manager prompt "No driver installed for this 
device", but install the driver "balloon.sys" failed.
     It said the driver is up to date.    Confused. (:

     How can I install and test the balloon driver on Windows?



The kvm-guest-drivers-windows.git on kernel.org is not available,is 
there any mirror git repository?
Any mail-list or bugzilla for windows guest driver?

Any help from will be appreciated.


-- 
Best Regards,
Cao,Bing Bu

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Arkady Frenkel]

On 11/21/2011 10:39 AM, Cao,Bing Bu wrote:
> Hi,
>
>     Recently,I am testing windows guest driver on Win7 and
> WinXP(32bit) with the latest windows guest driver development source.
>     Download from
> http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/
>
>
> virtio-blk:
>     It seems OK both on Win7 and WinXP,the r/w performance is better
> than IDE disk.
>
>
>
> virtio-serial:
>     I tried to test virtio serial driver using the test application in
> the project.
>
>     WinXP:
>     Write: OK
>     Read: Error: Read File Failed.
>
>     Win7:
>     The test application return error "can not find vioserial device".
>     But i debug the code and check that the GetDevicePath() return
> value is not NULL,and same as the value when testing on WinXP.
>     Why the CreateFile() in init() not called? (:
>
>
> virtio-balloon:
>
>     QEMU monitor: device_add virtio-balloon-pci
>
>     On the guest,a new device "PCI standard RAM controller" added.
>     But the Device Manager prompt "No driver installed for this
> device", but install the driver "balloon.sys" failed.
>     It said the driver is up to date.    Confused. (:
>
>     How can I install and test the balloon driver on Windows?
>
>
>
> The kvm-guest-drivers-windows.git on kernel.org is not available,is
> there any mirror git repository?
> Any mail-list or bugzilla for windows guest driver?
>
> Any help from will be appreciated.
>
>
You need to run serial test app as admin only.

To install balloon you have to go throw additional option when click on
"Browse my computer for driver software". Choose "Let me pick from the
list of device drivers on my computer" option.

Arkady

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Cao,Bing Bu]

[-- Attachment #1: Type: text/plain, Size: 2758 bytes --]

Hi,all


Thanks,Frenkel.The test application of the balloon must be run as admin.



But I found 2 problems(question) this week when testing windows guest 
drivers:


    *



     If only virtio serial driver installed,the virtio serial test app 
can not enumerate/find the virtio serial device,
     but after virtio balloon driver installed,the app can find the 
virtio serial device correctly.
     Because of the same GUID which balloon and serial both use?

*
*

    *


     When inflate/deflate the balloon size using qemu monitor balloon 
command,
     the total physical memory did not decrease/increase 
correspondingly,as seen from "resource monitor",
     only the "available memory" size descrease/increase.But I test on 
other Linux guest,
     the total physical memory of the guest OS was changed.

     Is it a problem? If not,is it confusing to user?
     Related to the windows internal memory management?




On 11/21/2011 06:33 PM, Arkady Frenkel wrote:
> On 11/21/2011 10:39 AM, Cao,Bing Bu wrote:
>> Hi,
>>
>>      Recently,I am testing windows guest driver on Win7 and
>> WinXP(32bit) with the latest windows guest driver development source.
>>      Download from
>> http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/
>>
>>
>> virtio-blk:
>>      It seems OK both on Win7 and WinXP,the r/w performance is better
>> than IDE disk.
>>
>>
>>
>> virtio-serial:
>>      I tried to test virtio serial driver using the test application in
>> the project.
>>
>>      WinXP:
>>      Write: OK
>>      Read: Error: Read File Failed.
>>
>>      Win7:
>>      The test application return error "can not find vioserial device".
>>      But i debug the code and check that the GetDevicePath() return
>> value is not NULL,and same as the value when testing on WinXP.
>>      Why the CreateFile() in init() not called? (:
>>
>>
>> virtio-balloon:
>>
>>      QEMU monitor: device_add virtio-balloon-pci
>>
>>      On the guest,a new device "PCI standard RAM controller" added.
>>      But the Device Manager prompt "No driver installed for this
>> device", but install the driver "balloon.sys" failed.
>>      It said the driver is up to date.    Confused. (:
>>
>>      How can I install and test the balloon driver on Windows?
>>
>>
>>
>> The kvm-guest-drivers-windows.git on kernel.org is not available,is
>> there any mirror git repository?
>> Any mail-list or bugzilla for windows guest driver?
>>
>> Any help from will be appreciated.
>>
>>
> You need to run serial test app as admin only.
>
> To install balloon you have to go throw additional option when click on
> "Browse my computer for driver software". Choose "Let me pick from the
> list of device drivers on my computer" option.
>
> Arkady
>

Best regards
Cao,Bing Bu


[-- Attachment #2: Type: text/html, Size: 3660 bytes --]

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Vadim Rozenfeld]

On Fri, 2011-11-25 at 09:59 +0800, Cao,Bing Bu wrote:
> Hi,all
> 
> 
> Thanks,Frenkel.The test application of the balloon must be run as
> admin.
> 
> 
> 
> But I found 2 problems(question) this week when testing windows guest
> drivers:
> 
> 
>       * 
>     If only virtio serial driver installed,the virtio serial test app
> can not enumerate/find the virtio serial device,
>     but after virtio balloon driver installed,the app can find the
> virtio serial device correctly.
>     Because of the same GUID which balloon and serial both use?
Correct. This test application is a very simplified one. We published it
mostly as an example, but not as a real test application. It doesn't
enumerate all virtio serial instances, rather just find the
first one and use it.   
> 
> 
> 
>       * 
>     When inflate/deflate the balloon size using qemu monitor balloon
> command,
>     the total physical memory did not decrease/increase
> correspondingly,as seen from "resource monitor",
>     only the "available memory" size descrease/increase.But I test on
> other Linux guest,
>     the total physical memory of the guest OS was changed.
> 
>     Is it a problem? If not,is it confusing to user?
>     Related to the windows internal memory management? 
> 
Total physical memory on Windows will always be the same,
because we don't hot-plug/unplug physical memory. 
Balloon driver works with non-paged pool memory instead.
So, every time you inflate or deflate balloon in your system,
you should see "Available memory" is changing, while physical 
will always be the same.

Best,
Vadim.

> 
> 
> 
> On 11/21/2011 06:33 PM, Arkady Frenkel wrote: 
> > On 11/21/2011 10:39 AM, Cao,Bing Bu wrote:
> > > Hi,
> > > 
> > >     Recently,I am testing windows guest driver on Win7 and
> > > WinXP(32bit) with the latest windows guest driver development source.
> > >     Download from
> > > http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/
> > > 
> > > 
> > > virtio-blk:
> > >     It seems OK both on Win7 and WinXP,the r/w performance is better
> > > than IDE disk.
> > > 
> > > 
> > > 
> > > virtio-serial:
> > >     I tried to test virtio serial driver using the test application in
> > > the project.
> > > 
> > >     WinXP:
> > >     Write: OK
> > >     Read: Error: Read File Failed.
> > > 
> > >     Win7:
> > >     The test application return error "can not find vioserial device".
> > >     But i debug the code and check that the GetDevicePath() return
> > > value is not NULL,and same as the value when testing on WinXP.
> > >     Why the CreateFile() in init() not called? (:
> > > 
> > > 
> > > virtio-balloon:
> > > 
> > >     QEMU monitor: device_add virtio-balloon-pci
> > > 
> > >     On the guest,a new device "PCI standard RAM controller" added.
> > >     But the Device Manager prompt "No driver installed for this
> > > device", but install the driver "balloon.sys" failed.
> > >     It said the driver is up to date.    Confused. (:
> > > 
> > >     How can I install and test the balloon driver on Windows?
> > > 
> > > 
> > > 
> > > The kvm-guest-drivers-windows.git on kernel.org is not available,is
> > > there any mirror git repository?
> > > Any mail-list or bugzilla for windows guest driver?
> > > 
> > > Any help from will be appreciated.
> > > 
> > > 
> > You need to run serial test app as admin only.
> > 
> > To install balloon you have to go throw additional option when click on
> > "Browse my computer for driver software". Choose "Let me pick from the
> > list of device drivers on my computer" option.
> > 
> > Arkady
> > 
> 
> Best regards
> Cao,Bing Bu
> 

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Cao,Bing Bu]

Hi,

     Rozenfeld,Thanks,got it!

     And do you know whether there are some sufficient test tools (such 
as IOmeter)
     to test the virtio driver performance?


On 11/25/2011 02:42 PM, Vadim Rozenfeld wrote:
> On Fri, 2011-11-25 at 09:59 +0800, Cao,Bing Bu wrote:
>> Hi,all
>>
>>
>> Thanks,Frenkel.The test application of the balloon must be run as
>> admin.
>>
>>
>>
>> But I found 2 problems(question) this week when testing windows guest
>> drivers:
>>
>>
>>        *
>>      If only virtio serial driver installed,the virtio serial test app
>> can not enumerate/find the virtio serial device,
>>      but after virtio balloon driver installed,the app can find the
>> virtio serial device correctly.
>>      Because of the same GUID which balloon and serial both use?
> Correct. This test application is a very simplified one. We published it
> mostly as an example, but not as a real test application. It doesn't
> enumerate all virtio serial instances, rather just find the
> first one and use it.
>>
>>
>>        *
>>      When inflate/deflate the balloon size using qemu monitor balloon
>> command,
>>      the total physical memory did not decrease/increase
>> correspondingly,as seen from "resource monitor",
>>      only the "available memory" size descrease/increase.But I test on
>> other Linux guest,
>>      the total physical memory of the guest OS was changed.
>>
>>      Is it a problem? If not,is it confusing to user?
>>      Related to the windows internal memory management?
>>
> Total physical memory on Windows will always be the same,
> because we don't hot-plug/unplug physical memory.
> Balloon driver works with non-paged pool memory instead.
> So, every time you inflate or deflate balloon in your system,
> you should see "Available memory" is changing, while physical
> will always be the same.
>
> Best,
> Vadim.
>
>>
>>
>> On 11/21/2011 06:33 PM, Arkady Frenkel wrote:
>>> On 11/21/2011 10:39 AM, Cao,Bing Bu wrote:
>>>> Hi,
>>>>
>>>>      Recently,I am testing windows guest driver on Win7 and
>>>> WinXP(32bit) with the latest windows guest driver development source.
>>>>      Download from
>>>> http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/
>>>>
>>>>
>>>> virtio-blk:
>>>>      It seems OK both on Win7 and WinXP,the r/w performance is better
>>>> than IDE disk.
>>>>
>>>>
>>>>
>>>> virtio-serial:
>>>>      I tried to test virtio serial driver using the test application in
>>>> the project.
>>>>
>>>>      WinXP:
>>>>      Write: OK
>>>>      Read: Error: Read File Failed.
>>>>
>>>>      Win7:
>>>>      The test application return error "can not find vioserial device".
>>>>      But i debug the code and check that the GetDevicePath() return
>>>> value is not NULL,and same as the value when testing on WinXP.
>>>>      Why the CreateFile() in init() not called? (:
>>>>
>>>>
>>>> virtio-balloon:
>>>>
>>>>      QEMU monitor: device_add virtio-balloon-pci
>>>>
>>>>      On the guest,a new device "PCI standard RAM controller" added.
>>>>      But the Device Manager prompt "No driver installed for this
>>>> device", but install the driver "balloon.sys" failed.
>>>>      It said the driver is up to date.    Confused. (:
>>>>
>>>>      How can I install and test the balloon driver on Windows?
>>>>
>>>>
>>>>
>>>> The kvm-guest-drivers-windows.git on kernel.org is not available,is
>>>> there any mirror git repository?
>>>> Any mail-list or bugzilla for windows guest driver?
>>>>
>>>> Any help from will be appreciated.
>>>>
>>>>
>>> You need to run serial test app as admin only.
>>>
>>> To install balloon you have to go throw additional option when click on
>>> "Browse my computer for driver software". Choose "Let me pick from the
>>> list of device drivers on my computer" option.
>>>
>>> Arkady
>>>
>> Best regards
>> Cao,Bing Bu
>>
>
>


-- 
Best Regards,
Cao,Bing Bu

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Vadim Rozenfeld]

On Tue, 2011-11-29 at 08:58 +0800, Cao,Bing Bu wrote:
> Hi,
> 
>      Rozenfeld,Thanks,got it!
> 
>      And do you know whether there are some sufficient test tools (such 
> as IOmeter)
>      to test the virtio driver performance?
IoMeter is good. But you also might be interested in 
SQLIOSim, database hammer, and diskio (part of WLK) + xperf.
> 
> 
> On 11/25/2011 02:42 PM, Vadim Rozenfeld wrote:
> > On Fri, 2011-11-25 at 09:59 +0800, Cao,Bing Bu wrote:
> >> Hi,all
> >>
> >>
> >> Thanks,Frenkel.The test application of the balloon must be run as
> >> admin.
> >>
> >>
> >>
> >> But I found 2 problems(question) this week when testing windows guest
> >> drivers:
> >>
> >>
> >>        *
> >>      If only virtio serial driver installed,the virtio serial test app
> >> can not enumerate/find the virtio serial device,
> >>      but after virtio balloon driver installed,the app can find the
> >> virtio serial device correctly.
> >>      Because of the same GUID which balloon and serial both use?
> > Correct. This test application is a very simplified one. We published it
> > mostly as an example, but not as a real test application. It doesn't
> > enumerate all virtio serial instances, rather just find the
> > first one and use it.
> >>
> >>
> >>        *
> >>      When inflate/deflate the balloon size using qemu monitor balloon
> >> command,
> >>      the total physical memory did not decrease/increase
> >> correspondingly,as seen from "resource monitor",
> >>      only the "available memory" size descrease/increase.But I test on
> >> other Linux guest,
> >>      the total physical memory of the guest OS was changed.
> >>
> >>      Is it a problem? If not,is it confusing to user?
> >>      Related to the windows internal memory management?
> >>
> > Total physical memory on Windows will always be the same,
> > because we don't hot-plug/unplug physical memory.
> > Balloon driver works with non-paged pool memory instead.
> > So, every time you inflate or deflate balloon in your system,
> > you should see "Available memory" is changing, while physical
> > will always be the same.
> >
> > Best,
> > Vadim.
> >
> >>
> >>
> >> On 11/21/2011 06:33 PM, Arkady Frenkel wrote:
> >>> On 11/21/2011 10:39 AM, Cao,Bing Bu wrote:
> >>>> Hi,
> >>>>
> >>>>      Recently,I am testing windows guest driver on Win7 and
> >>>> WinXP(32bit) with the latest windows guest driver development source.
> >>>>      Download from
> >>>> http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/
> >>>>
> >>>>
> >>>> virtio-blk:
> >>>>      It seems OK both on Win7 and WinXP,the r/w performance is better
> >>>> than IDE disk.
> >>>>
> >>>>
> >>>>
> >>>> virtio-serial:
> >>>>      I tried to test virtio serial driver using the test application in
> >>>> the project.
> >>>>
> >>>>      WinXP:
> >>>>      Write: OK
> >>>>      Read: Error: Read File Failed.
> >>>>
> >>>>      Win7:
> >>>>      The test application return error "can not find vioserial device".
> >>>>      But i debug the code and check that the GetDevicePath() return
> >>>> value is not NULL,and same as the value when testing on WinXP.
> >>>>      Why the CreateFile() in init() not called? (:
> >>>>
> >>>>
> >>>> virtio-balloon:
> >>>>
> >>>>      QEMU monitor: device_add virtio-balloon-pci
> >>>>
> >>>>      On the guest,a new device "PCI standard RAM controller" added.
> >>>>      But the Device Manager prompt "No driver installed for this
> >>>> device", but install the driver "balloon.sys" failed.
> >>>>      It said the driver is up to date.    Confused. (:
> >>>>
> >>>>      How can I install and test the balloon driver on Windows?
> >>>>
> >>>>
> >>>>
> >>>> The kvm-guest-drivers-windows.git on kernel.org is not available,is
> >>>> there any mirror git repository?
> >>>> Any mail-list or bugzilla for windows guest driver?
> >>>>
> >>>> Any help from will be appreciated.
> >>>>
> >>>>
> >>> You need to run serial test app as admin only.
> >>>
> >>> To install balloon you have to go throw additional option when click on
> >>> "Browse my computer for driver software". Choose "Let me pick from the
> >>> list of device drivers on my computer" option.
> >>>
> >>> Arkady
> >>>
> >> Best regards
> >> Cao,Bing Bu
> >>
> >
> >
> 
> 

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Cao,Bing Bu]

On 11/29/2011 08:36 PM, Vadim Rozenfeld wrote:
> On Tue, 2011-11-29 at 08:58 +0800, Cao,Bing Bu wrote:
>> Hi,
>>
>>       Rozenfeld,Thanks,got it!
>>
>>       And do you know whether there are some sufficient test tools (such
>> as IOmeter)
>>       to test the virtio driver performance?
> IoMeter is good. But you also might be interested in
> SQLIOSim, database hammer, and diskio (part of WLK) + xperf.
>>
>> On 11/25/2011 02:42 PM, Vadim Rozenfeld wrote:
>>> On Fri, 2011-11-25 at 09:59 +0800, Cao,Bing Bu wrote:
>>>> Hi,all
>>>>
>>>>
>>>> Thanks,Frenkel.The test application of the balloon must be run as
>>>> admin.
>>>>
>>>>
>>>>
>>>> But I found 2 problems(question) this week when testing windows guest
>>>> drivers:
>>>>
>>>>
>>>>         *
>>>>       If only virtio serial driver installed,the virtio serial test app
>>>> can not enumerate/find the virtio serial device,
>>>>       but after virtio balloon driver installed,the app can find the
>>>> virtio serial device correctly.
>>>>       Because of the same GUID which balloon and serial both use?
>>> Correct. This test application is a very simplified one. We published it
>>> mostly as an example, but not as a real test application. It doesn't
>>> enumerate all virtio serial instances, rather just find the
>>> first one and use it.
>>>>
>>>>         *
>>>>       When inflate/deflate the balloon size using qemu monitor balloon
>>>> command,
>>>>       the total physical memory did not decrease/increase
>>>> correspondingly,as seen from "resource monitor",
>>>>       only the "available memory" size descrease/increase.But I test on
>>>> other Linux guest,
>>>>       the total physical memory of the guest OS was changed.
>>>>
>>>>       Is it a problem? If not,is it confusing to user?
>>>>       Related to the windows internal memory management?
>>>>
>>> Total physical memory on Windows will always be the same,
>>> because we don't hot-plug/unplug physical memory.
>>> Balloon driver works with non-paged pool memory instead.
>>> So, every time you inflate or deflate balloon in your system,
>>> you should see "Available memory" is changing, while physical
>>> will always be the same.
>>>
>>> Best,
>>> Vadim.
>>>
>>>>
>>>> On 11/21/2011 06:33 PM, Arkady Frenkel wrote:
>>>>> On 11/21/2011 10:39 AM, Cao,Bing Bu wrote:
>>>>>> Hi,
>>>>>>
>>>>>>       Recently,I am testing windows guest driver on Win7 and
>>>>>> WinXP(32bit) with the latest windows guest driver development source.
>>>>>>       Download from
>>>>>> http://alt.fedoraproject.org/pub/alt/virtio-win/latest/images/src/
>>>>>>
>>>>>>
>>>>>> virtio-blk:
>>>>>>       It seems OK both on Win7 and WinXP,the r/w performance is better
>>>>>> than IDE disk.
>>>>>>
>>>>>>
>>>>>>
>>>>>> virtio-serial:
>>>>>>       I tried to test virtio serial driver using the test application in
>>>>>> the project.
>>>>>>
>>>>>>       WinXP:
>>>>>>       Write: OK
>>>>>>       Read: Error: Read File Failed.
>>>>>>
>>>>>>       Win7:
>>>>>>       The test application return error "can not find vioserial device".
>>>>>>       But i debug the code and check that the GetDevicePath() return
>>>>>> value is not NULL,and same as the value when testing on WinXP.
>>>>>>       Why the CreateFile() in init() not called? (:
>>>>>>
>>>>>>
>>>>>> virtio-balloon:
>>>>>>
>>>>>>       QEMU monitor: device_add virtio-balloon-pci
>>>>>>
>>>>>>       On the guest,a new device "PCI standard RAM controller" added.
>>>>>>       But the Device Manager prompt "No driver installed for this
>>>>>> device", but install the driver "balloon.sys" failed.
>>>>>>       It said the driver is up to date.    Confused. (:
>>>>>>
>>>>>>       How can I install and test the balloon driver on Windows?
>>>>>>
>>>>>>
>>>>>>
>>>>>> The kvm-guest-drivers-windows.git on kernel.org is not available,is
>>>>>> there any mirror git repository?
>>>>>> Any mail-list or bugzilla for windows guest driver?
>>>>>>
>>>>>> Any help from will be appreciated.
>>>>>>
>>>>>>
>>>>> You need to run serial test app as admin only.
>>>>>
>>>>> To install balloon you have to go throw additional option when click on
>>>>> "Browse my computer for driver software". Choose "Let me pick from the
>>>>> list of device drivers on my computer" option.
>>>>>
>>>>> Arkady
>>>>>
>>>> Best regards
>>>> Cao,Bing Bu
>>>>
>>>
>>
>
Thanks you,Vadim.(:

Is there anything TO-DO or need further optimization in current windows 
guest driver?
How could I contribute to the windows guest driver development(test 
patches,sign-off patches,bug fix,etc.)?

-- 
Best Regards,
Cao,Bing Bu

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Mark Wu]

> Total physical memory on Windows will always be the same,
> because we don't hot-plug/unplug physical memory.
> Balloon driver works with non-paged pool memory instead.
> So, every time you inflate or deflate balloon in your system,
> you should see "Available memory" is changing, while physical
> will always be the same.
But the behaviour of virtio-balloon is different on Linux guest. It 
updates the totalram_pages on deflate/inflate. Therefore the total 
physical memory will be updated in the system management interface even 
though it doesn't really hot-plug/unplug any physical memory.  If we 
just use 'info balloon' to query the balloon status, that should be 
fine. But if the VM management tool also collects  memory information 
from guest, it will become confusing.  Actually, I am not sure which one 
make more sense. I just think that it should have unified behaviour on 
both Linux and Windows guests.

Re: [Qemu-devel] windows guest virtio serial and balloon driver test issues

[Vadim Rozenfeld]

On Tue, 2011-11-29 at 10:43 +0800, Mark Wu wrote:
> > Total physical memory on Windows will always be the same,
> > because we don't hot-plug/unplug physical memory.
> > Balloon driver works with non-paged pool memory instead.
> > So, every time you inflate or deflate balloon in your system,
> > you should see "Available memory" is changing, while physical
> > will always be the same.
> But the behaviour of virtio-balloon is different on Linux guest. It 
> updates the totalram_pages on deflate/inflate. Therefore the total
In Windows MmNumberOfPhysicalPages is almost totally undocumented.
It doesn't mean you can't abuse it. But it will be a hack.
>  
> physical memory will be updated in the system management interface even 
> though it doesn't really hot-plug/unplug any physical memory.  If we 
> just use 'info balloon' to query the balloon status, that should be 
> fine. But if the VM management tool also collects  memory information 
> from guest, it will become confusing.  Actually, I am not sure which one 
> make more sense. I just think that it should have unified behaviour on 
> both Linux and Windows guests.
IMO VM management tools should reference to balloon actual size and
amount of available memory, retrieved from guest.