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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