White screen
Hi,
When using WinXP I get a completely white screen whenever I change the resolution and just before the Windows GUI comes up, which lasts for around 20 seconds. Also, as with Xen HVM, network performance is poor, although it seems to be faster than WinXP under Xen. Do you expect network performance to be good enough for server use in a guest in the future, maybe once the MMU has been improved, or will you go the same route as Xen and provide non-free guest network drivers?
Tested with stock linux-2.4.20-rc1 kvm modules and svn modules/qemu under Debian unstable.
Thanks
Mark.
PS. Highly impressive to have two WinXP windows playing full screen video in real time, and with plenty of cpu power left!
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Quoted 4 lines · Mark Clarkson
Hi,
When using WinXP I get a completely white screen whenever I change the resolution and just before the Windows GUI comes up, which lasts for around 20 seconds.
That is a known issue. Windows is clearing the screen using mmio writes. We have hacks to convert the mmio writes to regular RAM writes, but they aren't effective for the screen clearing. It is likely fixable, just haven't gotten around to it.
Quoted 6 lines
Also, as with Xen HVM, network performance is poor, although it seems to be faster than WinXP under Xen. Do you expect network performance to be good enough for server use in a guest in the future, maybe once the MMU has been improved, or will you go the same route as Xen and provide non-free guest network drivers?
We intend, at first, to improve fully virtualized performance as far as we are able, without resorting to paravirtualized drivers.
Should performance not be satisfactory to our needs, we may write paravirtualized devices and drivers. If we do so, I can't commit as to whether the paravirtualized Windows drivers will be open or not (I'm not saying the drivers will be closed -- just that no decision has been made).
However, if you (or anyone) is interested in writing paravirtulized drivers, we will work with you towards merging them into the kernel and into the kvm distribution. We welcome such contributions and will cooperate fully.
Signature · 8 lines
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Quoted 3 lines
Quoted 2 lines · Mark Clarkson
Hi,
When using WinXP I get a completely white screen whenever I change
the
Quoted 5 lines
Quoted 2 lines
resolution and just before the Windows GUI comes up, which lasts for around 20 seconds.
That is a known issue. Windows is clearing the screen using mmio writes. We have hacks to convert the mmio writes to regular RAM
writes,
Quoted 7 lines
but they aren't effective for the screen clearing. It is likely fixable, just haven't gotten around to it.
Quoted 3 lines
Also, as with Xen HVM, network performance is poor, although it seems to be faster than WinXP under Xen. Do you expect network performance to be good enough for server use in a guest in
the
Quoted 1 line
Quoted 1 line
future, maybe once the MMU has been improved, or will you go the
same
Quoted 4 lines
Quoted 2 lines
route as Xen and provide non-free guest network drivers?
We intend, at first, to improve fully virtualized performance as far
as
Quoted 4 lines
we are able, without resorting to paravirtualized drivers.
Should performance not be satisfactory to our needs, we may write paravirtualized devices and drivers. If we do so, I can't commit as
to
Quoted 1 line
whether the paravirtualized Windows drivers will be open or not (I'm
not
Quoted 1 line
saying the drivers will be closed -- just that no decision has been
made).
Quoted 3 lines
However, if you (or anyone) is interested in writing paravirtulized drivers, we will work with you towards merging them into the kernel
and
Quoted 3 lines
into the kvm distribution. We welcome such contributions and will cooperate fully.
Another future option would be to use hardware that support virtualization. There are already NICs (www.netxen.com) and HBAs that provide segmented virtual NICs per VM. They are not wide spread but they will be in the near future. The NIC vendor will provide the guest driver and we will add the VMM side.
Until then para-virtualizes drivers will have to be used.
Quoted 6 lines
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error compilingcommittee.c: too many arguments to function
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Quoted 12 lines · Avi Kivity
We intend, at first, to improve fully virtualized performance as far as
we are able, without resorting to paravirtualized drivers.Should performance not be satisfactory to our needs, we may write paravirtualized devices and drivers. If we do so, I can't commit as to
whether the paravirtualized Windows drivers will be open or not (I'm not
saying the drivers will be closed -- just that no decision has been made).
Quoted 5 lines
However, if you (or anyone) is interested in writing paravirtulized drivers, we will work with you towards merging them into the kernel and
into the kvm distribution. We welcome such contributions and will cooperate fully.
Unfortunately the slow network performance and the fact that, on my setup at least, network io takes 100% of a single core means that kvm is not currently useful for server use.
I really like the idea of kvm over Xen as it's a much 'cleaner' solution and would dearly love to see paravirtualised network drivers, at least for Linux guests, which would allow me to consider moving from Xen to kvm.
Do you think it possible/probable for someone with around 10 years knowledge of Linux and C programming but with no kernel module writing experience to be able to write a paravirtualised network driver for linux in under 6 months (in his/her spare time)? Is there any example code around for this? Would it be a case of say, modifying an ne2k driver? In fact, I've literally just seen that paravirtualised drivers exist for xen for linux 2.6 kernels and I presume these are open source
- could these be used in some way?
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Quoted 5 lines · Mark Clarkson
Unfortunately the slow network performance and the fact that, on my setup at least, network io takes 100% of a single core means that kvm is not currently useful for server use.
Certainly, kvm is slow right now for server use. This will improve quickly though.
Quoted 9 lines
I really like the idea of kvm over Xen as it's a much 'cleaner' solution and would dearly love to see paravirtualised network drivers, at least for Linux guests, which would allow me to consider moving from Xen to kvm.
Do you think it possible/probable for someone with around 10 years knowledge of Linux and C programming but with no kernel module writing experience to be able to write a paravirtualised network driver for linux in under 6 months (in his/her spare time)?
Well, it depends on how much spare time said someone is willing to commit. This is a fairly complex system. I will provide guidance however, should anyone require it.
For someone who is familiar with Linux and Windows networking, the task should take a few weeks.
Quoted 3 lines
Is there any example
code around for this? Would it be a case of say, modifying an ne2k driver?
Certainly that's the easiest way to start, as only the xmit/receive paths need to be accelerated.
Quoted 3 lines
In fact, I've literally just seen that paravirtualised drivers exist for xen for linux 2.6 kernels and I presume these are open source
I understand only the Linux guest drivers are open source.
The Xen paravirtualized drivers are quite complex and heavily tied to Xen (by using Xen features such as grant tables and event channels, which are all unnecessary for kvm). While we might borrow code from them, outright sharing is questionable.
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