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Re: [Qemu-discuss] what's the different for "qemu --eanble-kvm" and "acc


From: Stefan Hajnoczi
Subject: Re: [Qemu-discuss] what's the different for "qemu --eanble-kvm" and "accel=kvm" and "qemu(when kvm kmod load)"
Date: Mon, 7 Jan 2013 09:58:01 +0100

On Sun, Jan 6, 2013 at 12:27 PM, lei yang <address@hidden> wrote:
> What's the different with below combos?

The difference is historical, it's just how the command-line options
evolved over time.

> 1)qemu --enable-kvm

The old way.  Still useful because it's slightly easier to type than
--machine accel=kvm.

> 2)qemu accel=kvm

The "modern" way.

> 3)qemu without above parameters when kvm kmod has been load

There is a difference in behavior between QEMU and qemu-kvm here:

QEMU uses TCG and not KVM by default, regardless of whether the kvm.ko
module has been loaded or not.  qemu-kvm uses KVM by default, if
available.

The qemu-kvm fork has been retired so it's best not to rely on this
behavior.  Future distro packages will be built from QEMU and unless a
code change is made, the default accelerator is TCG.

Stefan



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