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

[Paolo Bonzini <pbonzini@redhat.com>]

On 11/07/2016 19:30, David Matlack wrote:
> On Mon, Jul 11, 2016 at 10:05 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>>
>> On 11/07/2016 18:51, David Matlack wrote:
>>>>> vcpus have statistics associated with them which can be viewed within the
>>>>> debugfs. Currently it is assumed within the vcpu_stat_get() and
>>>>> vcpu_stat_get_per_vm() functions that all of these statistics are
>>>>> represented as 32-bit numbers. The next patch adds some 64-bit statistics,
>>>>> so add provisioning for the display of 64-bit vcpu statistics.
>>> Thanks, we need 64-bit stats in other places as well. Can we use this
>>> opportunity to wholesale upgrade all KVM stats from u32 to u64? Most
>>> of this patch is duplicated code with "u32" swapped with "u64".
>>>
>>
>> I'm not sure of what 32-bit architectures would do, but perhaps we could
>> upgrade them to unsigned long at least.
> 
> 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.

Paolo