[PATCH rfc] nvme: support io stats on the mpath device

[Sagi Grimberg]

>>> 3. Do you have some performance numbers (we're touching the fast path
>>> here) ?
>>
>> This is pretty light-weight, accounting is per-cpu and only wrapped by
>> preemption disable. This is a very small price to pay for what we gain.
> 
> It does add up, though, and some environments disable stats to skip the
> overhead. At a minimum, you need to add a check for blk_queue_io_stat() before
> assuming you need to account for stats.

But QUEUE_FLAG_IO_STAT is set by nvme-mpath itself?
You mean disable IO stats in runtime?