[Qemu-devel] Re: qemu-kvm faster than qemu?

[walt <w41ter@gmail.com>]

On 08/25/2010 12:48 PM, Anthony Liguori wrote:
> On 08/25/2010 02:37 PM, walt wrote:
>> Hi qemu team,
>>
>> I just discovered that qemu now offers kvm support, so I decided to
>> compare it to qemu-kvm.
>>
>> I'm running the latest git versions of both programs on an AMD64
>> host running the latest kernel from Linus.git.
>>
>> The guest is Windows 7 on a qcow2 disk image and one kvm64 cpu.
>>
>> I find that qemu-kvm boots to the Win7 login prompt in 25 seconds,
 >> while qemu with kvm enabled takes about 45 seconds.
>
>
> make sure you build qemu with --enable-io-thread.

I built qemu both with and without io-thread, and it makes no difference
at least in this particular experiment.

(BTW, I found that qemu-kvm will not even compile with --enable-io-thread
because qemu_mutex_lock_iothread becomes defined in two places.)

> Also, what's your full command line?

For qemu:
/usr/local/bin/qemu-system-x86_64 -m 1024 -enable-kvm -cpu kvm64 w7.diff

For qemu-kvm:
/home/wa1ter/bin/qemu-system-x86_64 -m 1024 -enable-kvm -cpu kvm64 w7.diff

Note that w7.diff is the same file in both cases: a qcow2 differencing disk
made from the original qcow2 backing file w7.img.

Thanks for your reply.  I'm curious if anyone can reproduce this difference
in speed.