linux-kernel - Re: [PATCH RFC] scsi: ufs: Disable blk-mq for now

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Date:   Thu, 20 Sep 2018 08:58:04 +0200
From:   Christoph Hellwig <hch@....de>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.vnet.ibm.com>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Bart Van Assche <Bart.VanAssche@....com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        Stanislav Nijnikov <stanislav.nijnikov@....com>,
        Evan Green <evgreen@...omium.org>,
        Vinayak Holikatti <vinholikatti@...il.com>,
        Janek Kotas <jank@...ence.com>,
        Vivek Gautam <vivek.gautam@...eaurora.org>,
        Asutosh Das <asutoshd@...eaurora.org>,
        Subhash Jadavani <subhashj@...eaurora.org>,
        Sayali Lokhande <sayalil@...eaurora.org>,
        Li Wei <liwei213@...wei.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Alex Lemberg <Alex.Lemberg@...disk.com>
Subject: Re: [PATCH RFC] scsi: ufs: Disable blk-mq for now

On Fri, Sep 14, 2018 at 09:52:38AM +0800, Ming Lei wrote:
> However, in previous discussion, it is strongly objected to use
> per-driver/device .use_blk_mq switch, so not sure if this way can
> be accepted.

I don't like the per-driver switch as module_parameter at all and
we should never do that.  We had some exceptions for drivers to force
blk_mq (e.g. virtio), and given that I don't think we'll solve the
blk-mq runtime-pm issue for 4.19 and also don't want to revert the
default I think this patch is the best compromise for 4.19, with
a revert in 4.20 once we have runtime-pm for blk-mq.

So:

Acked-by: Christoph Hellwig <hch@....de>