[RFC PATCH 3/5] nvme-multipath: add sysfs attribute for adaptive I/O policy

[Hannes Reinecke]

On 9/21/25 13:12, Nilay Shroff wrote:
> This commit introduces a new sysfs attribute, "adp_stat", under the
> nvme path block device. This attribute provides visibility into the
> state of the adaptive I/O policy and is intended to aid debugging and
> observability. We now also calculate the per-path aggregated smoothed
> (EWMA) latency for reporting it under this new attribute.
> 
> The attribute reports per-path aggregated statistics, including I/O
> weight, smoothed (EWMA) latency, selection count, processed samples,
> and ignored samples.
> 
> Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
> ---
>   drivers/nvme/host/multipath.c | 77 ++++++++++++++++++++++++++++++++++-
>   drivers/nvme/host/nvme.h      |  2 +
>   drivers/nvme/host/sysfs.c     |  5 +++
>   3 files changed, 82 insertions(+), 2 deletions(-)
> 
Wouldn't this be better off if situated in the debugfs directly?
Exposing the stats is not really crucial to operations, and mainly
for debugging purposes only.

Exposing the weight from the EWMA algorithm, OTOH, really does influence
the performance, and might be an idea to expose.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
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