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From: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-kernel@vger.kernel.org,
	"open list:BLOCK LAYER" <linux-block@vger.kernel.org>
Subject: Re: [PATCH] block: elevator.c: Check elevator kernel argument again
Date: Sun, 14 Jul 2019 01:01:18 -0300
Message-ID: <20190714040118.GA19237@continental> (raw)
In-Reply-To: <75c5681a-389f-cfaf-7f3f-31a2daec9da4@kernel.dk>

On Sat, Jul 13, 2019 at 03:53:28PM -0600, Jens Axboe wrote:
> On 7/12/19 9:52 PM, Marcos Paulo de Souza wrote:
> > Since the inclusion of blk-mq, elevator= kernel argument was not being
> > considered anymore, making it impossible to specify a specific elevator
> > at boot time as it was used before.
> > 
> > This is done by checking chosen_elevator global variable, which is
> > populated once elevator= kernel argument is passed. Without this patch,
> > mq-deadline is the only elevator that is can be used at boot time.
> > 
> > Signed-off-by: Marcos Paulo de Souza <marcos.souza.org@gmail.com>
> > ---
> > 
> >   I found this issue while inspecting why noop scheduler was gone, and
> >   so I found that was now impossible to use a scheduler different from
> >   mq-deadeline.
> > 
> >   Am I missing something? Is this a desirable behavior?
> 
> Just google, I'm sure 2-3 discussions on this topic will come up.
> 
> tldr is that the original parameter was a mistake and doesn't work at
> all for multiple devices. Today it's even worse, as we have device
> types that won't even work properly with any scheduler, liked the
> zoned devices. The parameter was never enabled for blk-mq because of
> that, and hence died when the legacy IO path was scrapped. It's not
> coming back.

Thanks Jens. So it makes sense to remove all leftover code of elevator argument with
some dead documentation about it, avoiding confusion about it in the future
again. I will send some patches tomorrow.

> 
> -- 
> Jens Axboe
> 

      reply index

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-13  3:52 Marcos Paulo de Souza
2019-07-13 21:53 ` Jens Axboe
2019-07-14  4:01   ` Marcos Paulo de Souza [this message]

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