Re: [PATCH] block: Flag elevators suitable for single queue

[Linus Walleij <linus.walleij@xxxxxxxxxx>]

On Mon, Jun 1, 2020 at 9:50 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> On Thu, May 28, 2020 at 10:10:03AM +0200, Linus Walleij wrote:
> > The Kyber block scheduler is not suitable for single hardware
> > queue devices, so add a new flag for single hardware queue
> > devices and add that to the deadline and BFQ schedulers
> > so the Kyber scheduler will not be selected for single queue
> > devices.
>
> The above may not be true for some single hw queue high performance HBA(
> such as megasas), which can get better performance from none, so it is
> reasonable to get better performance from kyber, see 6ce3dd6eec11 ("blk-mq:
> issue directly if hw queue isn't busy in case of 'none'"), and the
> following link:
>
> https://lore.kernel.org/linux-block/20180710010331.27479-1-ming.lei@xxxxxxxxxx/

I see, but isn't the case rather that none is preferred and kyber gives
the same characteristics because it's not standing in the way
as much?

It looks like if we should add a special flag for these devices with
very fast single queues so they can say "I prefer none", do you
agree?

Yours,
Linus Walleij

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