Re: [Qemu-devel] Re: QEMU-KVM and video performance

[Jamie Lokier <jamie@shareable.org>]

Gerhard Wiesinger wrote:
> Can one switch to the old software vmm in VMWare?

Perhaps you can install a very old version of VMWare.
Maybe run it under KVM ;-)

> That was one of the reasons why I was looking for alternatives for 
> graphical DOS programs. Overall summary so far:
> 1.) QEMU without KVM: Problem with 286 DOS Extender instruction set, but 
> fast VGA
> 2.) QEMU with KVM: 286 DOS Extender apps ok, but slow VGA memory 
> performance
> 3.) VMWare Server 2.0 under Linux, application ok, but slow VGA memory 
> performance
> 4.) Virtual PC: Problems with 286 DOS Extender
> 5.) Bochs: Works well, but very slow.

I would be interested in the 286 DOS Extender issue, as I'd like to
use some 286 programs in QEMU at some point.

There were some changes to KVM in the kernel recently.  Were those
needed to get the 286 apps working?

> Looks like that VMWare Server and QEMU with KVM maybe have the same 
> architectural problems going through the whole slow chain from Guest OS to 
> virtualization layer for VGA writes.

They do have a similar architecture.

the VGA write speed is a bit surprising, as it should be fast in
256-colour non-modeX modes for both.  But maybe there's something
we've missed that makes it architecturally slow.  It will be
interesting to see what you find :-)

Thanks,
-- Jamie