Re: [PATCH v3 1/1] nvme: multipath: Implemented new iopolicy "queue-depth"

[John Meneghini]

On 5/21/24 02:46, Hannes Reinecke wrote:
> On 5/20/24 22:20, John Meneghini wrote:
> > From: "Ewan D. Milne" <emilne@xxxxxxxxxx>
..
> > Tested-by: Marco Patalano <mpatalan@xxxxxxxxxx>
> > Reviewed-by: Randy Jennings <randyj@xxxxxxxxxx>

I need to fix this. Randy doesn't have a redhat.com email address... Cut an paste error :-(

> > Tested-by: Jyoti Rani <jani@xxxxxxxxxxxxxxx>
..
> > +void nvme_subsys_iopolicy_update(struct nvme_subsystem *subsys, int iopolicy)
> > +{
> > +    struct nvme_ctrl *ctrl;
> > +    int old_iopolicy = READ_ONCE(subsys->iopolicy);
> > +
> > +    WRITE_ONCE(subsys->iopolicy, iopolicy);
> > +
> > +    mutex_lock(&nvme_subsystems_lock);
> > +    list_for_each_entry(ctrl, &subsys->ctrls, subsys_entry) {
> > +        atomic_set(&ctrl->nr_active, 0);
> > +        nvme_mpath_clear_ctrl_paths(ctrl);
>
> You always reset the variables here, even if specified iopolicy is
> the same than the currently active one.
> I'd rather check if the iopolicy is different before changing the settings.

Yes, Keith pointed this out too.  This is actually a feature not a bug.  In situations were we want to "reset" the nr_active 
counters on all controllers the user can simply set the queue-depth iopolicy a second time.  I don't expect users to do this 
very often... they shouldn't be changing IO policies back and forth too much... but the ability to "reset" the nr_active 
counters during testing has been very helpful and important to do.  So I'd like to keep this.  Moreover, this is NOT the 
performance path. I don't see the point in making performance optimizations in a code path that is run once a year.

/John