diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2022-07-12 17:49:17 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2022-09-12 07:55:06 +0300 |
| commit | 4f1d2a030db09af4d21695983674a18633cd0ffb (patch) | |
| tree | b149575bb927d0552a63441ab885a5a9128212f3 | |
| parent | 05c6257433b7212f07a7e53479a8ab038fc1666a (diff) | |
| download | linux-4f1d2a030db09af4d21695983674a18633cd0ffb.tar.xz | |
llist: use try_cmpxchg in llist_add_batch and llist_del_first
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
llist_add_batch and llist_del_first. x86 CMPXCHG instruction returns
success in ZF flag, so this change saves a compare after cmpxchg.
Also, try_cmpxchg implicitly assigns old *ptr value to "old" when cmpxchg
fails, enabling further code simplifications.
No functional change intended.
Link: https://lkml.kernel.org/r/20220712144917.4497-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | lib/llist.c | 12 |
1 files changed, 4 insertions, 8 deletions
diff --git a/lib/llist.c b/lib/llist.c index 611ce4881a87..7d78b736e8af 100644 --- a/lib/llist.c +++ b/lib/llist.c @@ -30,7 +30,7 @@ bool llist_add_batch(struct llist_node *new_first, struct llist_node *new_last, do { new_last->next = first = READ_ONCE(head->first); - } while (cmpxchg(&head->first, first, new_first) != first); + } while (!try_cmpxchg(&head->first, &first, new_first)); return !first; } @@ -52,18 +52,14 @@ EXPORT_SYMBOL_GPL(llist_add_batch); */ struct llist_node *llist_del_first(struct llist_head *head) { - struct llist_node *entry, *old_entry, *next; + struct llist_node *entry, *next; entry = smp_load_acquire(&head->first); - for (;;) { + do { if (entry == NULL) return NULL; - old_entry = entry; next = READ_ONCE(entry->next); - entry = cmpxchg(&head->first, old_entry, next); - if (entry == old_entry) - break; - } + } while (!try_cmpxchg(&head->first, &entry, next)); return entry; } |