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| author | Huang Ying <ying.huang@intel.com> | 2011-09-08 14:00:44 +0800 |
|---|---|---|
| committer | Ingo Molnar <mingo@elte.hu> | 2011-10-04 12:43:39 +0200 |
| commit | a3127336b71f6833d1483c856dce91fe558dc3a9 (patch) | |
| tree | c025279c450994f25661c2ab004f0be98997cf8a | |
| parent | 2c30245c65e8ebc3080b75ce65572ab8140bad0b (diff) | |
| download | linux-stable-a3127336b71f6833d1483c856dce91fe558dc3a9.tar.gz linux-stable-a3127336b71f6833d1483c856dce91fe558dc3a9.tar.bz2 linux-stable-a3127336b71f6833d1483c856dce91fe558dc3a9.zip | |
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.h | 7 | ||||
| -rw-r--r-- | lib/llist.c | 14 |
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; } |