blk-mq: Reuse hardware context cpumask for tags

BugLink: http://bugs.launchpad.net/bugs/1572630

hctx->cpumask is already populated and let the tag cpumask follow that
instead of going through a new for loop.
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
(cherry picked from commit e0e827b9)
Signed-off-by: Eric Desrochers <eric.desrochers@canonical.com>
Acked-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>

block/blk-mq.c

@@ -1857,6 +1857,7 @@ static void blk_mq_map_swqueue(struct request_queue *q,
 		hctx->tags = set->tags[i];
 		WARN_ON(!hctx->tags);
 
+		cpumask_copy(hctx->tags->cpumask, hctx->cpumask);
 		/*
 		 * Set the map size to the number of mapped software queues.
 		 * This is more accurate and more efficient than looping
@@ -1870,14 +1871,6 @@ static void blk_mq_map_swqueue(struct request_queue *q,
 		hctx->next_cpu = cpumask_first(hctx->cpumask);
 		hctx->next_cpu_batch = BLK_MQ_CPU_WORK_BATCH;
 	}
-
-	queue_for_each_ctx(q, ctx, i) {
-		if (!cpumask_test_cpu(i, online_mask))
-			continue;
-
-		hctx = q->mq_ops->map_queue(q, i);
-		cpumask_set_cpu(i, hctx->tags->cpumask);
-	}
 }
 
 static void queue_set_hctx_shared(struct request_queue *q, bool shared)