Commit 68c43f13 authored by Damien Le Moal's avatar Damien Le Moal Committed by Jens Axboe
Browse files

block: Introduce elevator features 



Introduce the definition of elevator features through the
elevator_features flags in the elevator_type structure. Each flag can
represent a feature supported by an elevator. The first feature defined
by this patch is support for zoned block device sequential write
constraint with the flag ELEVATOR_F_ZBD_SEQ_WRITE, which is implemented
by the mq-deadline elevator using zone write locking.

Other possible features are IO priorities, write hints, latency targets
or single-LUN dual-actuator disks (for which the elevator could maintain
one LBA ordered list per actuator).

The required_elevator_features field is also added to the request_queue
structure to allow a device driver to specify elevator feature flags
that an elevator must support for the correct operation of the device
(e.g. device drivers for zoned block devices can have the
ELEVATOR_F_ZBD_SEQ_WRITE flag as a required feature).
The helper function blk_queue_required_elevator_features() is
defined for setting this new field.

With these two new fields in place, the elevator functions
elevator_match() and elevator_find() are modified to allow a user to set
only an elevator with a set of features that satisfies the device
required features. Elevators not matching the device requirements are
not shown in the device sysfs queue/scheduler file to prevent their use.

The "none" elevator can always be selected as before.

Reviewed-by: default avatarJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Signed-off-by: default avatarDamien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 954b4a5c

block/blk-settings.c

+16 −0
Original line number Diff line number Diff line
@@ -832,6 +832,22 @@ void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua) 
}

EXPORT_SYMBOL_GPL(blk_queue_write_cache);



/**

 * blk_queue_required_elevator_features - Set a queue required elevator features

 * @q:		the request queue for the target device

 * @features:	Required elevator features OR'ed together

 *

 * Tell the block layer that for the device controlled through @q, only the

 * only elevators that can be used are those that implement at least the set of

 * features specified by @features.

 */

void blk_queue_required_elevator_features(struct request_queue *q,

					  unsigned int features)

{

	q->required_elevator_features = features;

}

EXPORT_SYMBOL_GPL(blk_queue_required_elevator_features);



static int __init blk_settings_init(void)

{

	blk_max_low_pfn = max_low_pfn - 1;

block/elevator.c

+38 −11
Original line number Diff line number Diff line
@@ -83,8 +83,26 @@ bool elv_bio_merge_ok(struct request *rq, struct bio *bio) 
}

EXPORT_SYMBOL(elv_bio_merge_ok);



static bool elevator_match(const struct elevator_type *e, const char *name)

static inline bool elv_support_features(unsigned int elv_features,

					unsigned int required_features)

{

	return (required_features & elv_features) == required_features;

}



/**

 * elevator_match - Test an elevator name and features

 * @e: Scheduler to test

 * @name: Elevator name to test

 * @required_features: Features that the elevator must provide

 *

 * Return true is the elevator @e name matches @name and if @e provides all the

 * the feratures spcified by @required_features.

 */

static bool elevator_match(const struct elevator_type *e, const char *name,

			   unsigned int required_features)

{

	if (!elv_support_features(e->elevator_features, required_features))

		return false;

	if (!strcmp(e->elevator_name, name))

		return true;

	if (e->elevator_alias && !strcmp(e->elevator_alias, name))
@@ -93,15 +111,21 @@ static bool elevator_match(const struct elevator_type *e, const char *name) 
	return false;

}



/*

 * Return scheduler with name 'name'

/**

 * elevator_find - Find an elevator

 * @name: Name of the elevator to find

 * @required_features: Features that the elevator must provide

 *

 * Return the first registered scheduler with name @name and supporting the

 * features @required_features and NULL otherwise.

 */

static struct elevator_type *elevator_find(const char *name)

static struct elevator_type *elevator_find(const char *name,

					   unsigned int required_features)

{

	struct elevator_type *e;



	list_for_each_entry(e, &elv_list, list) {

		if (elevator_match(e, name))

		if (elevator_match(e, name, required_features))

			return e;

	}
@@ -120,12 +144,12 @@ static struct elevator_type *elevator_get(struct request_queue *q, 


	spin_lock(&elv_list_lock);



	e = elevator_find(name);

	e = elevator_find(name, q->required_elevator_features);

	if (!e && try_loading) {

		spin_unlock(&elv_list_lock);

		request_module("%s-iosched", name);

		spin_lock(&elv_list_lock);

		e = elevator_find(name);

		e = elevator_find(name, q->required_elevator_features);

	}



	if (e && !try_module_get(e->elevator_owner))
@@ -525,7 +549,7 @@ int elv_register(struct elevator_type *e) 


	/* register, don't allow duplicate names */

	spin_lock(&elv_list_lock);

	if (elevator_find(e->elevator_name)) {

	if (elevator_find(e->elevator_name, 0)) {

		spin_unlock(&elv_list_lock);

		kmem_cache_destroy(e->icq_cache);

		return -EBUSY;
@@ -709,7 +733,8 @@ static int __elevator_change(struct request_queue *q, const char *name) 
	if (!e)

		return -EINVAL;



	if (q->elevator && elevator_match(q->elevator->type, elevator_name)) {

	if (q->elevator &&

	    elevator_match(q->elevator->type, elevator_name, 0)) {

		elevator_put(e);

		return 0;

	}
@@ -749,11 +774,13 @@ ssize_t elv_iosched_show(struct request_queue *q, char *name) 


	spin_lock(&elv_list_lock);

	list_for_each_entry(__e, &elv_list, list) {

		if (elv && elevator_match(elv, __e->elevator_name)) {

		if (elv && elevator_match(elv, __e->elevator_name, 0)) {

			len += sprintf(name+len, "[%s] ", elv->elevator_name);

			continue;

		}

		if (elv_support_iosched(q))

		if (elv_support_iosched(q) &&

		    elevator_match(__e, __e->elevator_name,

				   q->required_elevator_features))

			len += sprintf(name+len, "%s ", __e->elevator_name);

	}

	spin_unlock(&elv_list_lock);

block/mq-deadline.c

+1 −0
Original line number Diff line number Diff line
@@ -794,6 +794,7 @@ static struct elevator_type mq_deadline = { 
	.elevator_attrs = deadline_attrs,

	.elevator_name = "mq-deadline",

	.elevator_alias = "deadline",

	.elevator_features = ELEVATOR_F_ZBD_SEQ_WRITE,

	.elevator_owner = THIS_MODULE,

};

MODULE_ALIAS("mq-deadline-iosched");

include/linux/blkdev.h

+4 −0
Original line number Diff line number Diff line
@@ -496,6 +496,8 @@ struct request_queue { 


	struct queue_limits	limits;



	unsigned int		required_elevator_features;



#ifdef CONFIG_BLK_DEV_ZONED

	/*

	 * Zoned block device information for request dispatch control.
@@ -1097,6 +1099,8 @@ extern void blk_queue_dma_alignment(struct request_queue *, int); 
extern void blk_queue_update_dma_alignment(struct request_queue *, int);

extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);

extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);

extern void blk_queue_required_elevator_features(struct request_queue *q,

						 unsigned int features);



/*

 * Number of physical segments as sent to the device.

include/linux/elevator.h

+8 −0
Original line number Diff line number Diff line
@@ -76,6 +76,7 @@ struct elevator_type 
	struct elv_fs_entry *elevator_attrs;

	const char *elevator_name;

	const char *elevator_alias;

	const unsigned int elevator_features;

	struct module *elevator_owner;

#ifdef CONFIG_BLK_DEBUG_FS

	const struct blk_mq_debugfs_attr *queue_debugfs_attrs;
@@ -165,5 +166,12 @@ extern struct request *elv_rb_find(struct rb_root *, sector_t); 
#define rq_entry_fifo(ptr)	list_entry((ptr), struct request, queuelist)

#define rq_fifo_clear(rq)	list_del_init(&(rq)->queuelist)



/*

 * Elevator features.

 */



/* Supports zoned block devices sequential write constraint */

#define ELEVATOR_F_ZBD_SEQ_WRITE	(1U << 0)



#endif /* CONFIG_BLOCK */

#endif