From 4f1d2a030db09af4d21695983674a18633cd0ffb Mon Sep 17 00:00:00 2001 From: Uros Bizjak Date: Tue, 12 Jul 2022 16:49:17 +0200 Subject: [PATCH] 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 Signed-off-by: Andrew Morton --- lib/llist.c | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) diff --git a/lib/llist.c b/lib/llist.c index 611ce48..7d78b73 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; } -- 2.7.4