block: Improve default elevator selection

[linux.git] / block / elevator.c

diff --git a/block/elevator.c b/block/elevator.c
index 2944c129760ce56f060962132006aba1b0a4ed5e..520d6b224b74cd3c976f8ac30afb481abdda817b 100644 (file)
--- 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;
@@ -627,9 +651,46 @@ static inline bool elv_support_iosched(struct request_queue *q)
 }
 
 /*
- * For blk-mq devices supporting IO scheduling, we default to using mq-deadline,
- * if available, for single queue devices. If deadline isn't available OR
- * deadline initialization fails OR we have multiple queues, default to "none".
+ * For single queue devices, default to using mq-deadline. If we have multiple
+ * queues or mq-deadline is not available, default to "none".
+ */
+static struct elevator_type *elevator_get_default(struct request_queue *q)
+{
+       if (q->nr_hw_queues != 1)
+               return NULL;
+
+       return elevator_get(q, "mq-deadline", false);
+}
+
+/*
+ * Get the first elevator providing the features required by the request queue.
+ * Default to "none" if no matching elevator is found.
+ */
+static struct elevator_type *elevator_get_by_features(struct request_queue *q)
+{
+       struct elevator_type *e;
+
+       spin_lock(&elv_list_lock);
+
+       list_for_each_entry(e, &elv_list, list) {
+               if (elv_support_features(e->elevator_features,
+                                        q->required_elevator_features))
+                       break;
+       }
+
+       if (e && !try_module_get(e->elevator_owner))
+               e = NULL;
+
+       spin_unlock(&elv_list_lock);
+
+       return e;
+}
+
+/*
+ * For a device queue that has no required features, use the default elevator
+ * settings. Otherwise, use the first elevator available matching the required
+ * features. If no suitable elevator is find or if the chosen elevator
+ * initialization fails, fall back to the "none" elevator (no elevator).
  */
 void elevator_init_mq(struct request_queue *q)
 {
@@ -639,15 +700,15 @@ void elevator_init_mq(struct request_queue *q)
        if (!elv_support_iosched(q))
                return;
 
-       if (q->nr_hw_queues != 1)
-               return;
-
        WARN_ON_ONCE(test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags));
 
        if (unlikely(q->elevator))
                return;
 
-       e = elevator_get(q, "mq-deadline", false);
+       if (!q->required_elevator_features)
+               e = elevator_get_default(q);
+       else
+               e = elevator_get_by_features(q);
        if (!e)
                return;
 
@@ -709,7 +770,8 @@ 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 +811,13 @@ 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);