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authorHuang Ying <ying.huang@intel.com>2011-09-08 14:00:44 +0800
committerIngo Molnar <mingo@elte.hu>2011-10-04 12:43:39 +0200
commita3127336b71f6833d1483c856dce91fe558dc3a9 (patch)
treec025279c450994f25661c2ab004f0be98997cf8a
parent2c30245c65e8ebc3080b75ce65572ab8140bad0b (diff)
downloadlinux-linaro-stable-a3127336b71f6833d1483c856dce91fe558dc3a9.tar.gz
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: Huang Ying <ying.huang@intel.com> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1315461646-1379-4-git-send-email-ying.huang@intel.com Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--include/linux/llist.h7
-rw-r--r--lib/llist.c14
2 files changed, 15 insertions, 6 deletions
diff --git a/include/linux/llist.h b/include/linux/llist.h
index 65fca1cbf514..ca91875286bf 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -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);
+ }
}
/**
diff --git a/lib/llist.c b/lib/llist.c
index b445f2c8596a..6c69f1d14c4b 100644
--- a/lib/llist.c
+++ b/lib/llist.c
@@ -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;
}