[PATCH V2 4/5] kvm/stats: Add provisioning for 64-bit vcpu statistics

[Paolo Bonzini]

On 18/07/2016 09:17, Christian Borntraeger wrote:
> On 07/15/2016 09:52 AM, Suraj Jitindar Singh wrote:
>>
>>
>> On 14/07/16 19:42, Paolo Bonzini wrote:
>>>
>>> On 13/07/2016 20:00, Christian Borntraeger wrote:
>>>>>>>> I thought u64 still existed on 32-bit architectures. unsigned long
>>>>>>>> would be fine but with the caveat that certain stats would overflow on
>>>>>>>> 32-bit architectures.
>>>>>> Yes, but not all 32-bit architectures can do atomic read-modify-write
>>>>>> (e.g. add) operations on 64-bit values.
>>>> So what about only doing it for the VCPU events? Those should be only
>>>> modified by one CPU. We would have some odd values on 32bit overflow, but
>>>> this will be certainly better than just start with 0
>>> If that's good enough for PPC, that's fine.
>>>
>>> Paolo
>>
>> I'm don't feel great about having vcpu_stats as u64 and vm_stats still as u32
>> it's just a bit inconsistent.
>>
>> That being said, it's only the vcpu_stats which I require to be u64 at this
>> stage so it's possible to just upgrade those.
> 
> Yes, its not nice, but we probably want to avoid the overhead of atomics.
> What about using u64 for vcpu_stats and unsigned long for vm_stats. This will be
> correct for anyone and on 64bit systems we get 64 bits for everything?

That makes sense.

Paolo