[Qemu-devel] about -enable-kvm options

[Qemu-devel] about -enable-kvm options

[Gareth]

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Hi all

What does '-enable-kvm' option mean? I have heard two versions of answers:

a) guest OS would have /dev/kvm device and which could help vm in guest OS
(nested vm)
b) use /dev/kvm and intel-vt on host OS which could help vm run more fast
than pure emulator.

Thanks

-- 
Gareth

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Re: [Qemu-devel] about -enable-kvm options

[Jules Wang]

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I choose b)




在2014年08月01 11时15分, "Gareth"<academicgareth@gmail.com>写道:


Hi all


What does '-enable-kvm' option mean? I have heard two versions of answers:


a) guest OS would have /dev/kvm device and which could help vm in guest OS (nested vm)
b) use /dev/kvm and intel-vt on host OS which could help vm run more fast than pure emulator.  



Thanks


--

Gareth


Cloud Computing, OpenStack, Distributed Storage, Fitness, Basketball
OpenStack contributor, kun_huang@freenode
My promise: if you find any spelling or grammar mistakes in my email from Mar 1 2013, notify me 
and I'll donate $1 or ￥1 to an open organization you specify.

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Re: [Qemu-devel] about -enable-kvm options

[Richard W.M. Jones]

On Fri, Aug 01, 2014 at 11:15:29AM +0800, Gareth wrote:
> Hi all
> 
> What does '-enable-kvm' option mean? I have heard two versions of answers:

It's a shortcut for:

  $qemu -machine accel=kvm

> a) guest OS would have /dev/kvm device and which could help vm in guest OS
> (nested vm)

That's nested KVM, which is enabled as a module option in the kernel
module (on the host), eg:

  # modprobe kvm_intel nested=1

On AMD it's enabled by default.

> b) use /dev/kvm and intel-vt on host OS which could help vm run more fast
> than pure emulator.

Nearly.  It uses /dev/kvm on the host, which may or may not be
implemented using Intel VT, or a variety of other techniques.

You can also have fallbacks to software emulation (TCG):

  $qemu -machine accel=kvm:tcg

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-builder quickly builds VMs from scratch
http://libguestfs.org/virt-builder.1.html

Re: [Qemu-devel] about -enable-kvm options

[Gareth]

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Thanks Richard :)


On Sat, Aug 2, 2014 at 4:47 AM, Richard W.M. Jones <rjones@redhat.com>
wrote:

> On Fri, Aug 01, 2014 at 11:15:29AM +0800, Gareth wrote:
> > Hi all
> >
> > What does '-enable-kvm' option mean? I have heard two versions of
> answers:
>
> It's a shortcut for:
>
>   $qemu -machine accel=kvm
>
> > a) guest OS would have /dev/kvm device and which could help vm in guest
> OS
> > (nested vm)
>
> That's nested KVM, which is enabled as a module option in the kernel
> module (on the host), eg:
>
>   # modprobe kvm_intel nested=1
>
> On AMD it's enabled by default.
>
> > b) use /dev/kvm and intel-vt on host OS which could help vm run more fast
> > than pure emulator.
>
> Nearly.  It uses /dev/kvm on the host, which may or may not be
> implemented using Intel VT, or a variety of other techniques.
>
> You can also have fallbacks to software emulation (TCG):
>
>   $qemu -machine accel=kvm:tcg
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-builder quickly builds VMs from scratch
> http://libguestfs.org/virt-builder.1.html
>
>


-- 
Gareth

*Cloud Computing, OpenStack, Distributed Storage, Fitness, Basketball*
*OpenStack contributor, kun_huang@freenode*
*My promise: if you find any spelling or grammar mistakes in my email from
Mar 1 2013, notify me *
*and I'll donate $1 or ￥1 to an open organization you specify.*

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