[dm-devel] [PATCH v5 3/7] block: Introduce elevator features
Damien Le Moal
damien.lemoal at wdc.com
Thu Sep 5 09:51:31 UTC 2019
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.
Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
Reviewed-by: Johannes Thumshirn <jthumshirn at suse.de>
Reviewed-by: Christoph Hellwig <hch at lst.de>
---
block/blk-settings.c | 16 +++++++++++++
block/elevator.c | 49 +++++++++++++++++++++++++++++++---------
block/mq-deadline.c | 1 +
include/linux/blkdev.h | 4 ++++
include/linux/elevator.h | 8 +++++++
5 files changed, 67 insertions(+), 11 deletions(-)
diff --git a/block/blk-settings.c b/block/blk-settings.c
index a058997b9cce..6bd1e3b082d8 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -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;
diff --git a/block/elevator.c b/block/elevator.c
index 2944c129760c..ac7c8ad580ba 100644
--- a/block/elevator.c
+++ b/block/elevator.c
@@ -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);
diff --git a/block/mq-deadline.c b/block/mq-deadline.c
index 35e84bc0ec8c..b490f47fd553 100644
--- a/block/mq-deadline.c
+++ b/block/mq-deadline.c
@@ -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");
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index d0ad21e4771b..b196124e3240 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -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.
diff --git a/include/linux/elevator.h b/include/linux/elevator.h
index 1dd014c9c87b..901bda352dcb 100644
--- a/include/linux/elevator.h
+++ b/include/linux/elevator.h
@@ -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
--
2.21.0
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