block: get rid of blk-mq default scheduler choice Kconfig entries

The wording in the entries were poor and not understandable
by even deities. Kill the selection for default block scheduler,
and impose a policy with sane defaults.
Architected-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/Kconfig.iosched

@@ -69,50 +69,6 @@ config MQ_IOSCHED_DEADLINE
 	---help---
 	  MQ version of the deadline IO scheduler.
 
-config MQ_IOSCHED_NONE
-	bool
-	default y
-
-choice
-	prompt "Default single-queue blk-mq I/O scheduler"
-	default DEFAULT_SQ_NONE
-	help
-	  Select the I/O scheduler which will be used by default for blk-mq
-	  managed block devices with a single queue.
-
-	config DEFAULT_SQ_DEADLINE
-		bool "MQ Deadline" if MQ_IOSCHED_DEADLINE=y
-
-	config DEFAULT_SQ_NONE
-		bool "None"
-
-endchoice
-
-config DEFAULT_SQ_IOSCHED
-	string
-	default "mq-deadline" if DEFAULT_SQ_DEADLINE
-	default "none" if DEFAULT_SQ_NONE
-
-choice
-	prompt "Default multi-queue blk-mq I/O scheduler"
-	default DEFAULT_MQ_NONE
-	help
-	  Select the I/O scheduler which will be used by default for blk-mq
-	  managed block devices with multiple queues.
-
-	config DEFAULT_MQ_DEADLINE
-		bool "MQ Deadline" if MQ_IOSCHED_DEADLINE=y
-
-	config DEFAULT_MQ_NONE
-		bool "None"
-
-endchoice
-
-config DEFAULT_MQ_IOSCHED
-	string
-	default "mq-deadline" if DEFAULT_MQ_DEADLINE
-	default "none" if DEFAULT_MQ_NONE
-
 endmenu
 
 endif

block/blk-mq-sched.c

@@ -498,15 +498,6 @@ int blk_mq_sched_init(struct request_queue *q)
 {
 	int ret;
 
-#if defined(CONFIG_DEFAULT_SQ_NONE)
-	if (q->nr_hw_queues == 1)
-		return 0;
-#endif
-#if defined(CONFIG_DEFAULT_MQ_NONE)
-	if (q->nr_hw_queues > 1)
-		return 0;
-#endif
-
 	mutex_lock(&q->sysfs_lock);
 	ret = elevator_init(q, NULL);
 	mutex_unlock(&q->sysfs_lock);

block/elevator.c

@@ -220,17 +220,24 @@ int elevator_init(struct request_queue *q, char *name)
 	}
 
 	if (!e) {
-		if (q->mq_ops && q->nr_hw_queues == 1)
-			e = elevator_get(CONFIG_DEFAULT_SQ_IOSCHED, false);
-		else if (q->mq_ops)
-			e = elevator_get(CONFIG_DEFAULT_MQ_IOSCHED, false);
-		else
+		/*
+		 * For blk-mq devices, we default to using mq-deadline,
+		 * if available, for single queue devices. If deadline
+		 * isn't available OR we have multiple queues, default
+		 * to "none".
+		 */
+		if (q->mq_ops) {
+			if (q->nr_hw_queues == 1)
+				e = elevator_get("mq-deadline", false);
+			if (!e)
+				return 0;
+		} else
 			e = elevator_get(CONFIG_DEFAULT_IOSCHED, false);
 
 		if (!e) {
 			printk(KERN_ERR
 				"Default I/O scheduler not found. " \
-				"Using noop/none.\n");
+				"Using noop.\n");
 			e = elevator_get("noop", false);
 		}
 	}