nvme: split bios issued in reverse order

[Jonathan Nicklin]

On Tue, May 24, 2022 at 3:25 PM Keith Busch <kbusch at kernel.org> wrote:
>
> On Tue, May 24, 2022 at 12:12:29PM -0400, Jonathan Nicklin wrote:
> >
> > The command lines you have are for read operations. The behavior seems
> > only to appear with writes.
>
> Huh, I'll be darn...
>
> I think it's because the writes are plugged and the reads are not. The plug
> appends requests to the head of the plug list, and unplugging will dispatch the
> requests in the reverse order.

Thanks for confirming! That's about where I got to. Do you have any
ideas on what might explain the difference in behavior between
fio/pvsync and fio/libaio? And, why does this not seem to occur when
only one nvme queue is present? Perhaps the in-order cases are an
indication of not being plugged?