[PATCHv7 RFC 3/3] nvme-multipath: Add visibility for queue-depth io-policy

[Hannes Reinecke]

On 1/12/25 13:41, Nilay Shroff wrote:
> This patch helps add nvme native multipath visibility for queue-depth
> io-policy. It adds a new attribute file named "queue_depth" under
> namespace device path node which would print the number of active/
> in-flight I/O requests currently queued for the given path.
> 
> For instance, if we have a shared namespace accessible from two different
> controllers/paths then accessing head block node of the shared namespace
> would show the following output:
> 
> $ ls -l /sys/block/nvme1n1/multipath/
> nvme1c1n1 -> ../../../../../pci052e:78/052e:78:00.0/nvme/nvme1/nvme1c1n1
> nvme1c3n1 -> ../../../../../pci058e:78/058e:78:00.0/nvme/nvme3/nvme1c3n1
> 
> In the above example, nvme1n1 is head gendisk node created for a shared
> namespace and the namespace is accessible from nvme1c1n1 and nvme1c3n1
> paths. For queue-depth io-policy we can then refer the "queue_depth"
> attribute file created under each namespace path:
> 
> $ cat /sys/block/nvme1n1/multipath/nvme1c1n1/queue_depth
> 518
> 
> $cat /sys/block/nvme1n1/multipath/nvme1c3n1/queue_depth
> 504
> 
>>From the above output, we can infer that I/O workload targeted at nvme1n1
> uses two paths nvme1c1n1 and nvme1c3n1 and the current queue depth of each
> path is 518 and 504 respectively. Reading "queue_depth" file when
> configured io-policy is anything but queue-depth would show no output.
> 
> Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
> Signed-off-by: Nilay Shroff <nilay at linux.ibm.com>
> ---
>   drivers/nvme/host/multipath.c | 12 ++++++++++++
>   drivers/nvme/host/nvme.h      |  1 +
>   drivers/nvme/host/sysfs.c     |  3 ++-
>   3 files changed, 15 insertions(+), 1 deletion(-)
> 
Reviewed-by: Hannes Reinecke <hare at suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare at suse.de                                +49 911 74053 688
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