linux-kernel - Re: [PATCH V13 03/10] mmc: block: Add blk-mq support

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Date:   Fri, 10 Nov 2017 11:19:15 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>,
        Neil Brown <neilb@...e.com>, Ming Lei <ming.lei@...onical.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bough Chen <haibo.chen@....com>,
        Alex Lemberg <alex.lemberg@...disk.com>,
        Mateusz Nowak <mateusz.nowak@...el.com>,
        Yuliy Izrailov <Yuliy.Izrailov@...disk.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Dong Aisheng <dongas86@...il.com>,
        Das Asutosh <asutoshd@...eaurora.org>,
        Zhangfei Gao <zhangfei.gao@...il.com>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Harjani Ritesh <riteshh@...eaurora.org>,
        Venu Byravarasu <vbyravarasu@...dia.com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V13 03/10] mmc: block: Add blk-mq support

Following up on this:

On Thu, Nov 9, 2017 at 4:52 PM, Linus Walleij <linus.walleij@...aro.org> wrote:

>> No one has ever suggested that the legacy API will remain.  Once blk-mq is
>> ready the old code gets deleted.
>
> The block layer maintainers most definately think MQ is ready
> but you seem to disagree. Why?
>
> In the recent LWN article from kernel recepies:
> https://lwn.net/Articles/735275/
> the only obstacle I can see is a mention that SCSI was not
> switched over by default because of some problems with
> slow rotating media. "This change had to be backed out
> because of some performance and scalability issues that
> arose for rotating storage."
>
> Christoph mentions that he's gonna try again for v4.14.
> But it's true, I do not see that happening in linux-next yet.

Neil Brown's article on LWN points to Ming Lei's patch
set:
https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1513023.html

As addressing the issue that held back blk-MQ from
being default for SCSI, and it is reportedly to be
queued for v4.15. Since this MMC/SD rework is
also targeted for v4.15 I think we can assume it is
pretty much ready for everything, and delete the
non-MQ block path.

I just haven't seen any of this problem in my tests
with MMC/SD so I do not think it would be affected,
but it anyways seem to be fixed.

OK maybe I am especially optimistic. But it's not just
based on that.

Yours,
Linus Walleij