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Re: [Qemu-devel] [PATCH] Fix default CPU model for ARM64

From: Cole Robinson
Subject: Re: [Qemu-devel] [PATCH] Fix default CPU model for ARM64
Date: Thu, 07 May 2015 10:38:57 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.5.0

On 05/07/2015 02:36 AM, Pavel Fedin wrote:
>  Hello!
>> Yes. qemu-system-aarch64 -cpu cortex-a15 gets you a 32-bit Cortex-A15. This 
>> is
>> exactly like the x86 QEMU, where you can emulate all the 32-bit x86 CPUs in
>> qemu-system-x86_64.
>  And what is the default in x86_64 ? I believe it's 64-bit CPU, and not i686, 
> isn't it ?
>  I agree that -cpu cortex-a15 might work with qemu-system-aarch64. But isn't 
> it expected to get the "native" CPU by default ? This behavior of qemu causes 
> weird thing with libvirt/virt-manager. I create a VM, specify "aarch64" as 
> architecture, and set "hypervisor default" as CPU model. With "hypervisor 
> default" libvirt does not pass any -cpu option to qemu, leaving it up to the 
> emulator (exactly as expected). So, i supply 64-bit kernel and rootfs, and 
> nothing works. I have to explicitly change the CPU to "cortex-a57". Isn't it 
> confusing to have such a default ?
>  This is even more confusing since currently i don't know any implementation 
> of aarch64 except A57 and A53 (which are the same from software point of 
> view). So, i believe, A57 is quite a reasonable default.

FWIW virt-manager 1.2.0 (just released) will do the following when creating a
new VM:

- aarch64 + kvm : -cpu host
- aarch64 + tcg : -cpu cortex-a57
- arm32 + kvm : -cpu host
- arm32 + tcg : defer to qemu

Though if you explicitly request 'hypervisor default' then we won't specify
any -cpu and defer to qemu, which will hit the cortex-a15 default for aarch64

- Cole

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