Commit a3127336 authored by Huang Ying's avatar Huang Ying Committed by Ingo Molnar

llist: Move cpu_relax() to after the cmpxchg()

If in llist_add()/etc. functions the first cmpxchg() call succeeds, it is
not necessary to use cpu_relax() before the cmpxchg(). So cpu_relax() in
a busy loop involving cmpxchg() should go after cmpxchg() instead of before
that.

This patch fixes this for all involved llist functions.
Signed-off-by: default avatarHuang Ying <ying.huang@intel.com>
Acked-by: default avatarMathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1315461646-1379-4-git-send-email-ying.huang@intel.comSigned-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2c30245c
......@@ -148,11 +148,14 @@ static inline void llist_add(struct llist_node *new, struct llist_head *head)
struct llist_node *entry, *old_entry;
entry = head->first;
do {
for (;;) {
old_entry = entry;
new->next = entry;
entry = cmpxchg(&head->first, old_entry, new);
if (entry == old_entry)
break;
cpu_relax();
} while ((entry = cmpxchg(&head->first, old_entry, new)) != old_entry);
}
}
/**
......
......@@ -41,11 +41,14 @@ void llist_add_batch(struct llist_node *new_first, struct llist_node *new_last,
struct llist_node *entry, *old_entry;
entry = head->first;
do {
for (;;) {
old_entry = entry;
new_last->next = entry;
entry = cmpxchg(&head->first, old_entry, new_first);
if (entry == old_entry)
break;
cpu_relax();
} while ((entry = cmpxchg(&head->first, old_entry, new_first)) != old_entry);
}
}
EXPORT_SYMBOL_GPL(llist_add_batch);
......@@ -68,13 +71,16 @@ struct llist_node *llist_del_first(struct llist_head *head)
struct llist_node *entry, *old_entry, *next;
entry = head->first;
do {
for (;;) {
if (entry == NULL)
return NULL;
old_entry = entry;
next = entry->next;
entry = cmpxchg(&head->first, old_entry, next);
if (entry == old_entry)
break;
cpu_relax();
} while ((entry = cmpxchg(&head->first, old_entry, next)) != old_entry);
}
return entry;
}
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment