[gentoo-user] Best way for good video performance in virtual machines

[gentoo-user] Best way for good video performance in virtual machines

[Ralf]

Hi out there,

assume the following situation:

I do have a minimalistic hypervisor running a minimalistic virtual
machine (qemu with kvm, qxl and spice).
Both systems, hypervisor and VM are able to run X servers and apllications.
The graphics card of the hypervisor is connected to a monitor. This
monitor only has to show one single standalone QT application which is
running on the virtual machine.

What will give me more video performance?

1. Running a minimalistic X server on the virtual machine showing the
application AND running a minimalistic X server on the hypervisor
running remote-viewer
or
2. Running a minimalistic X server on the hypervisor and using
X11-Forwarding via bridged ethernet

Or maybe even someone knows a better solution?

Thank you folks!

Cheers
  Ralf

Re: [gentoo-user] Best way for good video performance in virtual machines

[R0b0t1]

What will the Qt application be doing? Any of those setups should be
sufficient for a typical GUI program.

Highest performance would probably be passing a discrete card to the
guest... not particularly the smartest move, but it would account for
every usecase. Barring that, #2 should have the least amount of
overhead, as X11 does the drawing on the system running the server (so
host's GPU instead of guest's virtual GPU).

Re: [gentoo-user] Best way for good video performance in virtual machines

[wabenbau]

Ralf <ralf+gentoo@ramses-pyramidenbau.de> wrote:

> Hi out there,
> 
> assume the following situation:
> 
> I do have a minimalistic hypervisor running a minimalistic virtual
> machine (qemu with kvm, qxl and spice).
> Both systems, hypervisor and VM are able to run X servers and
> apllications. The graphics card of the hypervisor is connected to a
> monitor. This monitor only has to show one single standalone QT
> application which is running on the virtual machine.
> 
> What will give me more video performance?
> 
> 1. Running a minimalistic X server on the virtual machine showing the
> application AND running a minimalistic X server on the hypervisor
> running remote-viewer
> or
> 2. Running a minimalistic X server on the hypervisor and using
> X11-Forwarding via bridged ethernet
> 
> Or maybe even someone knows a better solution?
> 
> Thank you folks!
> 
> Cheers
>   Ralf

On my system, qemu-kvm has the best performance with X11 on guest. 
I've also tested vnc and spice with qxl video driver on guest, but X11 
was faster.

I can imagine that this depends on the hardware and screen resolution.
So maybe on your system an other setup is better.

My host GPU is a Radeon Ultimate R7 250, resolution is 3840x2160@60Hz, 
driver is xf86-video-ati.
X11 compositing is deactivated on host as well as on guest. 

As "video card" on guest I use vmware (-vga vmware). Screen resolution 
on guest is 2386x1770. That seems to be the highest possible screen size
that is available with this settings. I also tested other guest video
drivers (std and cirrus) but vmware was the fastest and also the one with
the highest resolution.

Before I bought an UHD monitor, I used sdl as qemu display (-display sdl)
in borderless fullscreen mode (-no-frame -full-screen). I used the same 
screen resolution on host and guest (1920x1200) and qemu was running on 
one of my virtual XFCE desktops. 
This was very handy. But as I've written before, it seems not possible for
me to run qemu with UHD screen size. So fullscreen mode isn't possible any
longer and now qemu runs in a window on my desktop (-display gtk).

But with none of my setups it was/is possible to run a fullscreen video
on the guest vm. Performance is much to slow for that. I've spent some
time to make it faster, but I failed. 

I would be happy for any hints about better video performance with qemu.

--
Regards
wabe

Re: [gentoo-user] Best way for good video performance in virtual machines

[Ralf]

On 06/25/2015 01:29 AM, R0b0t1 wrote:
> What will the Qt application be doing? Any of those setups should be
> sufficient for a typical GUI program.
>
> Highest performance would probably be passing a discrete card to the
> guest... not particularly the smartest move, but it would account for
> every usecase. Barring that, #2 should have the least amount of
> overhead, as X11 does the drawing on the system running the server (so
> host's GPU instead of guest's virtual GPU).
>
Well, the QT Application will have to show WebViews using WebKit which
contain Flash content.

Do NOT ask why, just accept it (so do I...) :-D

Does qemu actually support passing a whole graphics card? Never tried it.

Thx and cheers

Re: [gentoo-user] Best way for good video performance in virtual machines

[Ralf]

Oh, I forgot about the gtk and sdl displays... I'll test them together
with QXL.

Thanks for your hint!

But anyways, I'll need two X servers when using this setup - one on the
VM and one on the hypervisor.
Shouldn't X11 forwarding be less overhead?

Thank you
  Ralf

On 06/25/2015 05:44 AM, wabenbau@gmail.com wrote:
> Ralf <ralf+gentoo@ramses-pyramidenbau.de> wrote:
>
>> Hi out there,
>>
>> assume the following situation:
>>
>> I do have a minimalistic hypervisor running a minimalistic virtual
>> machine (qemu with kvm, qxl and spice).
>> Both systems, hypervisor and VM are able to run X servers and
>> apllications. The graphics card of the hypervisor is connected to a
>> monitor. This monitor only has to show one single standalone QT
>> application which is running on the virtual machine.
>>
>> What will give me more video performance?
>>
>> 1. Running a minimalistic X server on the virtual machine showing the
>> application AND running a minimalistic X server on the hypervisor
>> running remote-viewer
>> or
>> 2. Running a minimalistic X server on the hypervisor and using
>> X11-Forwarding via bridged ethernet
>>
>> Or maybe even someone knows a better solution?
>>
>> Thank you folks!
>>
>> Cheers
>>   Ralf
> On my system, qemu-kvm has the best performance with X11 on guest. 
> I've also tested vnc and spice with qxl video driver on guest, but X11 
> was faster.
>
> I can imagine that this depends on the hardware and screen resolution.
> So maybe on your system an other setup is better.
>
> My host GPU is a Radeon Ultimate R7 250, resolution is 3840x2160@60Hz, 
> driver is xf86-video-ati.
> X11 compositing is deactivated on host as well as on guest. 
>
> As "video card" on guest I use vmware (-vga vmware). Screen resolution 
> on guest is 2386x1770. That seems to be the highest possible screen size
> that is available with this settings. I also tested other guest video
> drivers (std and cirrus) but vmware was the fastest and also the one with
> the highest resolution.
>
> Before I bought an UHD monitor, I used sdl as qemu display (-display sdl)
> in borderless fullscreen mode (-no-frame -full-screen). I used the same 
> screen resolution on host and guest (1920x1200) and qemu was running on 
> one of my virtual XFCE desktops. 
> This was very handy. But as I've written before, it seems not possible for
> me to run qemu with UHD screen size. So fullscreen mode isn't possible any
> longer and now qemu runs in a window on my desktop (-display gtk).
>
> But with none of my setups it was/is possible to run a fullscreen video
> on the guest vm. Performance is much to slow for that. I've spent some
> time to make it faster, but I failed. 
>
> I would be happy for any hints about better video performance with qemu.
>
> --
> Regards
> wabe
>

Re: [gentoo-user] Best way for good video performance in virtual machines

[Matti Nykyri]

> On Jun 25, 2015, at 11:47, Ralf <ralf+gentoo@ramses-pyramidenbau.de> wrote:
> 
>> On 06/25/2015 01:29 AM, R0b0t1 wrote:
>> What will the Qt application be doing? Any of those setups should be
>> sufficient for a typical GUI program.
>> 
>> Highest performance would probably be passing a discrete card to the
>> guest... not particularly the smartest move, but it would account for
>> every usecase. Barring that, #2 should have the least amount of
>> overhead, as X11 does the drawing on the system running the server (so
>> host's GPU instead of guest's virtual GPU).
> Well, the QT Application will have to show WebViews using WebKit which
> contain Flash content.
> 
> Do NOT ask why, just accept it (so do I...) :-D
> 
> Does qemu actually support passing a whole graphics card? Never tried it.

Yes it does. For examlpe if you have a windows client and pass the card to it the client can utilize directx and you get nearly native 3d performance in the games within the client. In that case the client owns the graphics card and the has to have another one should it require one...

-- 
-Matti