linux-kernel - Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra scheduler

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Message-ID: <3d0b38bb-537d-94ff-574f-587bad949fdd@kernel.dk>
Date:   Fri, 28 Oct 2016 09:30:07 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Linus Walleij <linus.walleij@...aro.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Paolo Valente <paolo.valente@...aro.org>,
        Christoph Hellwig <hch@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Bart Van Assche <bart.vanassche@...disk.com>,
        Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
        linux-block@...r.kernel.org,
        Linux-Kernal <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Hannes Reinecke <hare@...e.de>,
        Grant Likely <grant.likely@...retlab.ca>,
        James Bottomley <James.Bottomley@...senpartnership.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH 00/14] introduce the BFQ-v0 I/O scheduler as an extra
 scheduler

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