[RFC PATCHv2 4/4] nvme-multipath: add debugfs attribute for adaptive I/O policy stat

[Nilay Shroff]

On 10/16/25 1:57 PM, Daniel Wagner wrote:
> On Thu, Oct 16, 2025 at 08:14:19AM +0200, Hannes Reinecke wrote:
>>> Currently queue_depth and numa_nodes attributes are created under
>>> sysfs, so do you meant to move those attributes from sysfs to
>>> debugfs?
>>>
>> Yes. sysfs information can be perused by udev rules, and that assumes
>> the information in there will not change without a 'CHANGE' uevent.
>> So it's questionable whether volatile information like the queue depth
>> or the round-robin path selection should be presented there.
>> I'd rather have it moved into debugfs.
>>
>> But that might be personal preference.
> 
> If this moves to debugfs, I think nvme-cli should not show it per
> default. Don't want to get lots of questions why the value is not
> showed or updated.

That’s a fair concern — debugfs isn’t guaranteed to be available in
production systems (it may be disabled or not mounted), so depending
on it from nvme-cli would be unreliable. Given that, I think it’s
safer to keep queue_depth and numa_node in sysfs for now since they’re
already part of the sysfs and used by nvme-cli.

Thanks,
--Nilay