Re: [PATCH v5 31/36] vfio/migration: Add x-migration-multifd-transfer VFIO property

[Avihai Horon <avihaih@nvidia.com>]

On 04/03/2025 0:17, Maciej S. Szmigiero wrote:
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>
>
> On 2.03.2025 15:48, Avihai Horon wrote:
>>
>> On 19/02/2025 22:34, Maciej S. Szmigiero wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>
>>>
>>> This property allows configuring at runtime whether to transfer the
>>
>> IIUC, in this patch it's not configurable at runtime, so let's drop 
>> "at runtime".
>
> Dropped this expression from this patch description.
>
>>> particular device state via multifd channels when live migrating that
>>> device.
>>>
>>> It defaults to AUTO, which means that VFIO device state transfer via
>>> multifd channels is attempted in configurations that otherwise 
>>> support it.
>>>
>>> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
>>> ---
>>>   hw/vfio/migration-multifd.c   | 17 ++++++++++++++++-
>>>   hw/vfio/pci.c                 |  3 +++
>>>   include/hw/vfio/vfio-common.h |  2 ++
>>>   3 files changed, 21 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/hw/vfio/migration-multifd.c b/hw/vfio/migration-multifd.c
>>> index 0cfa9d31732a..18a5ff964a37 100644
>>> --- a/hw/vfio/migration-multifd.c
>>> +++ b/hw/vfio/migration-multifd.c
>>> @@ -460,11 +460,26 @@ bool vfio_multifd_transfer_supported(void)
>>>
>>>   bool vfio_multifd_transfer_enabled(VFIODevice *vbasedev)
>>>   {
>>> -    return false;
>>> +    VFIOMigration *migration = vbasedev->migration;
>>> +
>>> +    return migration->multifd_transfer;
>>>   }
>>>
>>>   bool vfio_multifd_transfer_setup(VFIODevice *vbasedev, Error **errp)
>>>   {
>>> +    VFIOMigration *migration = vbasedev->migration;
>>> +
>>> +    /*
>>> +     * Make a copy of this setting at the start in case it is changed
>>> +     * mid-migration.
>>> +     */
>>> +    if (vbasedev->migration_multifd_transfer == ON_OFF_AUTO_AUTO) {
>>> +        migration->multifd_transfer = 
>>> vfio_multifd_transfer_supported();
>>> +    } else {
>>> +        migration->multifd_transfer =
>>> +            vbasedev->migration_multifd_transfer == ON_OFF_AUTO_ON;
>>> +    }
>>
>> Making a copy of this value is only relevant for the next patch where 
>> it's turned mutable, so let's move this code to patch #32.
>
> But we still need to handle the "AUTO" condition so it would need
> very similar code just to get reworked into the above in the next
> patch.
> I think that's just not worth code churn between patches.

Ah, I understand.
In that case, we can move only the comment "Make a copy of this setting 
..." to patch #32.

Thanks.