- The single finisher of a bluestore can be a bottleneck when using an SSD as a backend device. If too much load is given to the single finisher, client-side IO latency increases. So we add multiple finishers to the bluestore, which shows better performance.
- ‘bluestore_finisher_threads' option is added to be able to configure the number of finisher threads.

Signed-off-by: Ilsoo Byun <ilsoo.byun@sk.com>

- a finisher is selected according to the shard id of a sequencer.
- the number of finishers is decided by osd_op_num_shards.
- 'bluestore_use_multiple_finishers' option is added to be able to configure wheather finsihers is multiple or not.
- 'bluetore_finisher_threads' option is removed.

Signed-off-by: Ilsoo Byun <ilsoo.byun@sk.com>

- The single finisher of a bluestore can be a bottleneck when using an SSD as a backend device. If too much load is given to the single finisher, client-side IO latency increases. So we add multiple finishers to the bluestore, which shows better performance.
- 'bluestore_use_multiple_finishers' option is added to be able to configure wheather finsihers is multiple or not.
- a finisher is selected according to the shard id of a sequencer.
- the number of finishers is decided by osd_op_num_shards.

Signed-off-by: Ilsoo Byun <ilsoo.byun@sk.com>

…to multi_finisher