linux-kernel - Re: [PATCH V9 13/15] mmc: block: Add CQE and blk-mq support

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Date:   Wed, 4 Oct 2017 11:48:27 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        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 V9 13/15] mmc: block: Add CQE and blk-mq support

[...]

>> MQ code that doesn't perform and therefore we cannot switch seamlessly
>> to MQ.
>
> I think that switching seamlessly to blk-mq in short/medium-term
> is not possible (SCSI tried and failed to do so). The changes to
> the old path are very complex and besides affecting performance
> they also affect error recovery handling (which needs to be tested
> properly before the switch).

Agreed, and that's why I have queued up the new Kconfig option for
enabling the blkmq path from MMC.

Kind regards
Uffe