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Re: [Qemu-discuss] qemu for windows and kvm

From: Jakob Bohm
Subject: Re: [Qemu-discuss] qemu for windows and kvm
Date: Tue, 26 Feb 2013 14:34:40 +0100
User-agent: Mozilla/5.0 (Windows NT 5.2; WOW64; rv:17.0) Gecko/20130215 Thunderbird/17.0.3

On 2/26/2013 5:06 AM, Sylvain wrote:
 Hi all,

I had a good experiment a few years ago
with qemu-0.9.1 for windows
I recently decided to update to the latest version which
is 1.3.1 .

On my windows vista laptop
 (AMD athlon 64 dual core if it can help), I was able to run successfully
the sample bat file linux-0.2.bat .

I adapted my old .bat script
for my application. It worked but very slowly.
I decided to activate the kvm acceleration.
It failed with the message:

KVM not supported for this target
No accelerator found!

Here is the content of the .bat file :

REM Start qemu on windows.
REM net start kqemu

START qemu-system-x86_64w.exe -L Bios -k en-us -vga std -m 512M -sdl -soundhw es1370 ^
-boot menu=off,order=dca ^
-rtc base=localtime,clock=host ^
-name RACD -drive file=linux-0.2.img,media=disk,cache=writeback ^
-net nic,model=ne2k_pci -net user -enable-kvm ^
-machine pc,accel=kvm,kernel_irqchip=on -cpu pentium ^
-cdrom 1.2.4.iso

(I obtained similar results using qemu-system-i386w.exe instead of qemu-system-x86_64w.exe )

In the past, it was necessary to install kqemu for windows
(the three commented lines at the beginning of the script are a sequel of that; the behavior
is not changed if these lines are uncommented)

Is it necessary to update kqemu for windows ?
(the old one which was working properly with qemu-0.9.x is still there)
Or is the problem elsewhere ?

Unfortunately, shortly after kqemu was opensourced, some short-sighted
person decided thatbecause some expensive CPUs, under Linux only,
could get better results with kvm, thenall the kqemu support should be
removed from qemu.

This has left us all with no CPU assisted acceleration of
same-architecture qemu in all of thefollowing scenarios:

 - x86 CPUs without virtual extensions
 - non-Linux kernels
 - nested virtualisation
 - non-x86 CPUs that could have had kqemu-like functionality (which is
  almost all CPUs with hardware separation of user and kernel mode).

Whether or not based on the old kqemu, there is a generic need for a
mechanism that will run user mode guest code natively, by somehow
(depending on OS) asking the host kernel to set the user mode memory
layout to match what the Guest has told the virtual qemu CPU to do
and to trap all forms of exceptions and system call mechanisms back
to qemu.


Jakob Bohm, CIO, Partner, WiseMo A/S.  http://www.wisemo.com
Transformervej 29, 2730 Herlev, Denmark.  Direct +45 31 13 16 10
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WiseMo - Remote Service Management for PCs, Phones and Embedded

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