Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra
 scheduler
To: Linus Walleij <linus.walleij@linaro.org>
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Cc: Ulf Hansson <ulf.hansson@linaro.org>,
        Paolo Valente <paolo.valente@linaro.org>,
        Christoph Hellwig <hch@infradead.org>, Arnd Bergmann <arnd@arndb.de>,
        Bart Van Assche <bart.vanassche@sandisk.com>, Jan Kara <jack@suse.cz>,
        Tejun Heo <tj@kernel.org>, linux-block@vger.kernel.org,
        Linux-Kernal <linux-kernel@vger.kernel.org>,
        Mark Brown <broonie@kernel.org>, Hannes Reinecke <hare@suse.de>,
        Grant Likely <grant.likely@secretlab.ca>,
        James Bottomley <James.Bottomley@hansenpartnership.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
From: Jens Axboe <axboe@kernel.dk>
Message-ID: <3d0b38bb-537d-94ff-574f-587bad949fdd@kernel.dk>
Date: Fri, 28 Oct 2016 09:30:07 -0600
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On 10/28/2016 03:32 AM, Linus Walleij wrote:
> The patch to enable MQ looks like this:
> https://git.kernel.org/cgit/linux/kernel/git/linusw/linux-stericsson.git/commit/?h=mmc-mq&id=8f79b527e2e854071d8da019451da68d4753f71d

BTW, another viable "hack" for the depth issue would be to expose more
than one hardware queue. It's meant to map to a distinct submission
region in the hardware, but there's nothing stopping the driver from
using it differently. Might not be cleaner than just increasing the
queue depth on a single queue, though.

That still won't solve the issue of lying about it and causing IO
scheduler confusion, of course.

Also, 4.8 and newer have support for BLK_MQ_F_BLOCKING, if you need to
block in ->queue_rq(). That could eliminate the need to offload to a
kthread manually.

-- 
Jens Axboe