From 56e3d1cd05cc7b24cfcae8714b0661bf607aaba3 Mon Sep 17 00:00:00 2001 From: "Jason A. Donenfeld" Date: Thu, 15 Dec 2016 06:01:10 +0100 Subject: [PATCH] kref: prefer atomic_inc_not_zero to atomic_add_unless On most platforms, there exists this ifdef: #define atomic_inc_not_zero(v) atomic_add_unless((v), 1, 0) This makes this patch functionally useless. However, on PPC, there is actually an explicit definition of atomic_inc_not_zero with its own assembly that is slightly more optimized than atomic_add_unless. So, this patch changes kref to use atomic_inc_not_zero instead, for PPC and any future platforms that might provide an explicit implementation. This also puts this usage of kref more in line with a verbatim reading of the examples in Paul McKenney's paper [1] in the section titled "2.4 Atomic Counting With Check and Release Memory Barrier", which uses atomic_inc_not_zero. [1] http://open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2167.pdf Signed-off-by: Jason A. Donenfeld Reviewed-by: Thomas Hellstrom Signed-off-by: Daniel Vetter Link: http://patchwork.freedesktop.org/patch/msgid/20161215050110.3241-1-Jason@zx2c4.com --- include/linux/kref.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/kref.h b/include/linux/kref.h index e15828f..62f0a84 100644 --- a/include/linux/kref.h +++ b/include/linux/kref.h @@ -133,6 +133,6 @@ static inline int kref_put_mutex(struct kref *kref, */ static inline int __must_check kref_get_unless_zero(struct kref *kref) { - return atomic_add_unless(&kref->refcount, 1, 0); + return atomic_inc_not_zero(&kref->refcount); } #endif /* _KREF_H_ */ -- 2.7.4