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

[walt <w41ter@gmail.com>]

On 08/25/2010 04:28 PM, Anthony Liguori wrote:
> On 08/25/2010 06:09 PM, walt wrote:
>> On 08/25/2010 12:48 PM, Anthony Liguori wrote:
>>> On 08/25/2010 02:37 PM, walt wrote:

>>>> I find that qemu-kvm boots to the Win7 login prompt in 25 seconds,
>>>> while qemu with kvm enabled takes about 45 seconds.

>>> Also, what's your full command line?

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

> You'll get more accurate and repeatable results by using:
>
> qemu-system-x86_64 -m 1024 -enable-kvm -cpu kvm64 -drive file=w7.diff,cache=none

Turning off the cache slows both of them down, as I would expect:

qemu-kvm:  52 seconds
qemu:      65 seconds

> Also try qemu-kvm with -no-kvm-irqchip. I can't believe an in-kernel lapic would make this much of a difference with windows 7 but it's worth trying.

Using that flag wipes out the difference entirely:  both come in at about 65 seconds.

I also tried xp-32 running on the same two kvm64 virtual machines, with slightly
different results:

qemu-kvm:  35 seconds (65 seconds using -no-kvm-irqchip, a huge disadvantage)
qemu:      58 seconds

Anything unexpected in these results?

Thanks for your time.