On Wed, Oct 3, 2018 at 9:05 AM Artem Bityutskiy [off-list ref] wrote:

On Wed, 2018-10-03 at 08:29 +0200, Paolo Valente wrote:

quoted

So, I do understand your need for conservativeness, but, after so much
evidence on single-queue devices, and so many years! :), what's the
point in keeping Linux worse for virtually everybody, by default?

Sounds like what we just need a mechanism for the device (ubi block in
this case) to select the I/O scheduler. I doubt enhancing the default
scheduler selection logic in 'elevator.c' is the right answer. Just
give the driver authority to override the defaults.

This might be true in the wider sense (like for what scheduler to
select for an NVME device with N channels) but $SUBJECT is just
trying to select BFQ (if available) for devices with one and only one
hardware queue.

That is AFAICT the only reasonable choice for anything with just
one hardware queue as things stand right now.

I have a slight reservation for the weird outliers like loopdev, which
has "one hardware queue" (.nr_hw_queues == 1) though this
makes no sense at all. So I would like to know what people think
about that. Maybe we should have .nr_queues and .nr_hw_queues
where the former is the number of logical queues and the latter
the actual number of hardware queues.

Yours,
Linus Walleij