Re: [PATCH v5 19/36] vfio/migration: Convert bytes_transferred counter to atomic

["Cédric Le Goater" <clg@redhat.com>]

On 2/26/25 14:55, Maciej S. Szmigiero wrote:
> On 26.02.2025 08:52, Cédric Le Goater wrote:
>> On 2/19/25 21:34, Maciej S. Szmigiero wrote:
>>> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>>>
>>> So it can be safety accessed from multiple threads.
>>>
>>> This variable type needs to be changed to unsigned long since
>>> 32-bit host platforms lack the necessary addition atomics on 64-bit
>>> variables.
>>>
>>> Using 32-bit counters on 32-bit host platforms should not be a problem
>>> in practice since they can't realistically address more memory anyway.
>>
>> Is it useful to have VFIO on 32-bit host platforms ?
>>
>> If not, VFIO PCI should depend on (AARCH64 || PPC64 || X86_64) and we
>> could drop this patch. Let's address that independently.
> 
> Not sure how much use VFIO gets on 32-bit host platforms,
> however totally disabling it on these would be a major functional regression -
> at least if taken at its face value.

32-bit host platform support is being deprecated in QEMU 10.0 and should
be removed in QEMU 10.2.

> Especially considering that making it work on 32-bit platform requires
> just this tiny variable type change here.

yes. It raised my attention because x86 32-bit was the only host platform
I was not sure about and Alex confirmed it worked. We should simply wait
for removal.


Thanks,

C.