llist: Return whether list is empty before adding in llist_add()
Extend the llist_add*() functions to return a success indicator, this
allows us in the scheduler code to send an IPI if the queue was empty.
( There's no effect on existing users, because the list_add_xxx() functions
are inline, thus this will be optimized out by the compiler if not used
by callers. )
Signed-off-by: Huang Ying <ying.huang@intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1315461646-1379-5-git-send-email-ying.huang@intel.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/include/linux/llist.h b/include/linux/llist.h
index ca91875..27bbdf5 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -142,8 +142,10 @@
* llist_add - add a new entry
* @new: new entry to be added
* @head: the head for your lock-less list
+ *
+ * Return whether list is empty before adding.
*/
-static inline void llist_add(struct llist_node *new, struct llist_head *head)
+static inline bool llist_add(struct llist_node *new, struct llist_head *head)
{
struct llist_node *entry, *old_entry;
@@ -156,6 +158,8 @@
break;
cpu_relax();
}
+
+ return old_entry == NULL;
}
/**
diff --git a/lib/llist.c b/lib/llist.c
index 6c69f1d..878985c 100644
--- a/lib/llist.c
+++ b/lib/llist.c
@@ -34,8 +34,10 @@
* @new_first: first entry in batch to be added
* @new_last: last entry in batch to be added
* @head: the head for your lock-less list
+ *
+ * Return whether list is empty before adding.
*/
-void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
+bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
struct llist_head *head)
{
struct llist_node *entry, *old_entry;
@@ -49,6 +51,8 @@
break;
cpu_relax();
}
+
+ return old_entry == NULL;
}
EXPORT_SYMBOL_GPL(llist_add_batch);