Re: [Qemu-devel] [PATCH] resent: x86/cpuid: propagate further CPUID leafs when -cpu host

[Avi Kivity <avi@redhat.com>]

On 05/25/2010 01:10 AM, Anthony Liguori wrote:
> On 05/21/2010 02:50 AM, Andre Przywara wrote:
>> -cpu host currently only propagates the CPU's family/model/stepping,
>> the brand name and the feature bits.
>> Add a whitelist of safe CPUID leafs to let the guest see the actual
>> CPU's cache details and other things.
>>
>> Signed-off-by: Andre Przywara<andre.przywara@amd.com>
>
> The problem I can see is that this greatly increases the chances of 
> problems with live migration since we don't migrate the cpuid state.

-cpu host is already problematic for live migration.

Are you talking about the state maintained by the cpuid instruction?  
Yes, we need to migrate those bits.

>
> What's the benefit of exposing this information to the guest?
>

Some algorithms adjust themselves based on the cache size.  If you have 
several passes over a large data set, it's often better to run each set 
of passes on a subset of the dataset that fits in cache, then stitch the 
subsets together.

-- 
error compiling committee.c: too many arguments to function