From b55841807fb864eccca0167650a65722fd7cd553 Mon Sep 17 00:00:00 2001
From: Ilya Dryomov <idryomov@gmail.com>
Date: Tue, 23 Jun 2015 16:21:19 +0300
Subject: [PATCH] rbd: queue_depth map option

nr_requests (/sys/block/rbd<id>/queue/nr_requests) is pretty much
irrelevant in blk-mq case because each driver sets its own max depth
that it can handle and that's the number of tags that gets preallocated
on setup.  Users can't increase queue depth beyond that value via
writing to nr_requests.

For rbd we are happy with the default BLKDEV_MAX_RQ (128) for most
cases but we want to give users the opportunity to increase it.
Introduce a new per-device queue_depth option to do just that:

    $ sudo rbd map -o queue_depth=1024 ...

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Alex Elder <elder@linaro.org>
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