QEMU vs KVM

QEMU vs KVM

[gerryw-dHy0zPTSVEVBDgjK7y7TUQ]

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Hello All,

I am a bit unclear about the differences between QEMU and KVM. If I 
understand correctly, QEMU can run in a mode on an x86 where it executes 
user space code directly on the cpu without emulation. This seems to be 
very similar to what KVM is doing with the exception of using the 
virtualization capability of the cpu. I would think there would be very 
little difference in performance between the two in this case. Please 
forgive my ignorance, because I don't know that much about the new VT cpus 
yet. What is the actual difference / objective of the KVM project?

Thanks,
-G






 

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Re: QEMU vs KVM

[Avi Kivity]

gerryw-dHy0zPTSVEVBDgjK7y7TUQ@public.gmane.org wrote:
>
> Hello All,
>
> I am a bit unclear about the differences between QEMU and KVM. If I 
> understand correctly, QEMU can run in a mode on an x86 where it 
> executes user space code directly on the cpu without emulation. This 
> seems to be very similar to what KVM is doing with the exception of 
> using the virtualization capability of the cpu. I would think there 
> would be very little difference in performance between the two in this 
> case. Please forgive my ignorance, because I don't know that much 
> about the new VT cpus yet. What is the actual difference / objective 
> of the KVM project?

You're describing kqemu, not qemu.

Qemu is an emulator; it can emualte a large number of guests on a large 
number of hosts, albeit at fairly slow speeds.

kqemu is a "qemu accelerator" which can be used to speed up qemu 
emulation if the guest and host are the same.

kvm is a hardware virtualization system that is part of the Linux 
kernel.  While at present the only serious user is a modified qemu, it 
is not tied to qemu.  It is faster than either qemu of kqemu.  The 
downside is that it requires hardware virtualization extensions for 
fully virtualized guests.



-- 
error compiling committee.c: too many arguments to function


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Re: QEMU vs KVM

[gerryw-dHy0zPTSVEVBDgjK7y7TUQ]

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Hi,

Thanks! Sorry. Yes. I meant kqemu.

Okay.. so would it be correct to say that kqemu formed the initial base of 
what is now kvm/kvm_intel/kvm_amd and that the mods to qemu are necessary 
for interfacing to the kernel drivers and possibly some paravirtualized 
drivers for enhanced I/O performance?

Also.. when you say that kvm is part of the linux kernel do you mean 
2.6.20 and above? Are the modules no longer necessary for the .20+ 
kernels?

I know your very busy. I really appreciate your taking the time to answer 
my questions.

Thanks Again,
-G






 



Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> 
09/12/2007 04:04 AM

To
gerryw-dHy0zPTSVEVBDgjK7y7TUQ@public.gmane.org
cc
kvm-devel <kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
Subject
Re: [kvm-devel] QEMU vs KVM






gerryw-dHy0zPTSVEVBDgjK7y7TUQ@public.gmane.org wrote:
>
> Hello All,
>
> I am a bit unclear about the differences between QEMU and KVM. If I 
> understand correctly, QEMU can run in a mode on an x86 where it 
> executes user space code directly on the cpu without emulation. This 
> seems to be very similar to what KVM is doing with the exception of 
> using the virtualization capability of the cpu. I would think there 
> would be very little difference in performance between the two in this 
> case. Please forgive my ignorance, because I don't know that much 
> about the new VT cpus yet. What is the actual difference / objective 
> of the KVM project?

You're describing kqemu, not qemu.

Qemu is an emulator; it can emualte a large number of guests on a large 
number of hosts, albeit at fairly slow speeds.

kqemu is a "qemu accelerator" which can be used to speed up qemu 
emulation if the guest and host are the same.

kvm is a hardware virtualization system that is part of the Linux 
kernel.  While at present the only serious user is a modified qemu, it 
is not tied to qemu.  It is faster than either qemu of kqemu.  The 
downside is that it requires hardware virtualization extensions for 
fully virtualized guests.



-- 
error compiling committee.c: too many arguments to function



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_______________________________________________
kvm-devel mailing list
kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
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Re: QEMU vs KVM

[Avi Kivity]

gerryw-dHy0zPTSVEVBDgjK7y7TUQ@public.gmane.org wrote:
>
> Hi,
>
> Thanks! Sorry. Yes. I meant kqemu.
>
> Okay.. so would it be correct to say that kqemu formed the initial 
> base of what is now kvm/kvm_intel/kvm_amd 

No.

> and that the mods to qemu are necessary for interfacing to the kernel 
> drivers and possibly some paravirtualized drivers for enhanced I/O 
> performance?

Yes.

>
> Also.. when you say that kvm is part of the linux kernel do you mean 
> 2.6.20 and above?

Yes.

> Are the modules no longer necessary for the .20+ kernels?

They are included in .20+.

>
> I know your very busy. I really appreciate your taking the time to 
> answer my questions.
>
> Thanks Again,
> -G
>
>
>
>
>
>  
>
>
> *Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>*
>
> 09/12/2007 04:04 AM
>
> 	
> To
> 	gerryw-dHy0zPTSVEVBDgjK7y7TUQ@public.gmane.org
> cc
> 	kvm-devel <kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
> Subject
> 	Re: [kvm-devel] QEMU vs KVM
>
>
>
> 	
>
>
>
>
>
> gerryw-dHy0zPTSVEVBDgjK7y7TUQ@public.gmane.org wrote:
> >
> > Hello All,
> >
> > I am a bit unclear about the differences between QEMU and KVM. If I
> > understand correctly, QEMU can run in a mode on an x86 where it
> > executes user space code directly on the cpu without emulation. This
> > seems to be very similar to what KVM is doing with the exception of
> > using the virtualization capability of the cpu. I would think there
> > would be very little difference in performance between the two in this
> > case. Please forgive my ignorance, because I don't know that much
> > about the new VT cpus yet. What is the actual difference / objective
> > of the KVM project?
>
> You're describing kqemu, not qemu.
>
> Qemu is an emulator; it can emualte a large number of guests on a large
> number of hosts, albeit at fairly slow speeds.
>
> kqemu is a "qemu accelerator" which can be used to speed up qemu
> emulation if the guest and host are the same.
>
> kvm is a hardware virtualization system that is part of the Linux
> kernel.  While at present the only serious user is a modified qemu, it
> is not tied to qemu.  It is faster than either qemu of kqemu.  The
> downside is that it requires hardware virtualization extensions for
> fully virtualized guests.
>
>
>
> -- 
> error compiling committee.c: too many arguments to function
>
>


-- 
error compiling committee.c: too many arguments to function


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