Re: [Qemu-devel] cpuid problem in upstream qemu with kvm

[Dor Laor <dlaor@redhat.com>]

On 01/07/2010 10:18 AM, Avi Kivity wrote:
> On 01/07/2010 10:03 AM, Dor Laor wrote:
>>
>> We can debate about the exact name/model to represent the Nehalem
>> family, I don't have an issue with that and actually Intel and Amd
>> should define it.
>
> AMD and Intel already defined their names (in cat /proc/cpuinfo). They
> don't define families, the whole idea is to segment the market.

The idea here is to minimize the number of models we should have the 
following range for Intel for example:
   pentium3 - merom -  penry - Nehalem - host - kvm/qemu64
So we're supplying wide range of cpus, p3 for maximum flexibility and 
migration, nehalem for performance and migration, host for maximum 
performance and qemu/kvm64 for custom maid.

>
>>
>> There are two main motivations behind the above approach:
>> 1. Sound guest cpu definition.
>> Using a predefined model should automatically set all the relevant
>> vendor/stepping/cpuid flags/cache sizes/etc.
>> We just can let every management application deal with it. It breaks
>> guest OS/apps. For instance there are MSI support in windows guest
>> relay on the stepping.
>>
>> 2. Simplifying end user and mgmt tools.
>> qemu/kvm have the best knowledge about these low levels. If we push
>> it up in the stack, eventually it reaches the user. The end user,
>> not a 'qemu-devel user' which is actually far better from the
>> average user.
>>
>> This means that such users will have to know what is popcount and
>> whether or not to limit migration on one host by adding sse4.2 or
>> not.
>>
>> This is exactly what vmware are doing:
>> - Intel CPUs :
>> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1991
>>
>> - AMD CPUs :
>> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1992
>>
>
> They don't have to deal with different qemu and kvm versions.
>

Both our customers - the end users. It's not their problem.
IMO what's missing today is a safe and sound cpu emulation that is 
simply and friendly to represent. qemu64,+popcount is not simple for the 
end user. There is no reason to through it on higher level mgmt.