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

[Nilay Shroff]

On 10/13/25 12:03 PM, Hannes Reinecke wrote:
> On 10/9/25 12:05, Nilay Shroff wrote:
>> This commit introduces a new debugfs attribute, "adaptive_stat", under
>> both per-path and head debugfs directories (defined under /sys/kernel/
>> debug/block/). This attribute provides visibility into the internal
>> state of the adaptive I/O policy to aid in debugging and performance
>> analysis.
>>
>> For per-path entries, "adaptive_stat" reports the corresponding path
>> statistics such as I/O weight, selection count, processed samples, and
>> ignored samples.
>>
>> For head entries, it reports per-CPU statistics for each reachable path,
>> including I/O weight, path score, smoothed (EWMA) latency, selection
>> count, processed samples, and ignored samples.
>>
>> These additions enhance observability of the adaptive I/O path selection
>> behavior and help diagnose imbalance or instability in multipath
>> performance.
>>
>> Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
>> ---
>>   drivers/nvme/host/core.c      |   3 +
>>   drivers/nvme/host/debugfs.c   | 117 ++++++++++++++++++++++++++++++++++
>>   drivers/nvme/host/multipath.c |   2 +
>>   3 files changed, 122 insertions(+)
>>
> Reviewed-by: Hannes Reinecke <hare at suse.de>
> 
> Might be an idea to have support for queue-depth in here, too.
> 
Currently queue_depth and numa_nodes attributes are created under 
sysfs, so do you meant to move those attributes from sysfs to 
debugfs? 

Thanks,
--Nilay