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

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Date:   Fri, 14 Sep 2018 09:52:38 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     "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 Thu, Sep 13, 2018 at 03:15:39PM +0300, Adrian Hunter wrote:
> On 13/09/18 15:05, Ming Lei wrote:
> > On Thu, Sep 13, 2018 at 02:28:48PM +0300, Adrian Hunter wrote:
> >> blk-mq does not support runtime pm, so disable blk-mq support for now.
> > 
> > So could you describe a bit what the issue you are trying to fix?
> 
> UFS is a low-power solution, so we must be able to runtime suspend.
> 
> > 
> > This is host level runtime PM you are trying to address, and if blk-mq
> > runtime isn't enabled, I guess the host won't be runtime suspended at all
> > because some of its descendant are always active.
> > 
> > So seems we need to do nothing for preventing the host controller from
> > entering runtime suspend.
> 
> We don't want to prevent the host controller from runtime suspending, quite
> the opposite.

OK, got it.

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.

BTW, I just posted the runtime PM enablement patches[1] for blk-mq,
and I verified that it works fine and passed blktests & xfstest & my
other sanity tests, could you try it on UFS?

[1] https://marc.info/?l=linux-block&m=153684095523409&w=2

Thanks,
Ming