From b78c0d471255e99411d6c1b3975df21c3cd9f349 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 1 Feb 2017 16:07:55 +0100 Subject: [PATCH] locking/refcounts: Use atomic_try_cmpxchg() Generates better code (GCC-6.2.1): text filename 1576 defconfig-build/lib/refcount.o.pre 1488 defconfig-build/lib/refcount.o.post Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- lib/refcount.c | 47 +++++++++++++++-------------------------------- 1 file changed, 15 insertions(+), 32 deletions(-) diff --git a/lib/refcount.c b/lib/refcount.c index 8e206ce5609b..f42124ccf295 100644 --- a/lib/refcount.c +++ b/lib/refcount.c @@ -57,9 +57,9 @@ */ bool refcount_add_not_zero(unsigned int i, refcount_t *r) { - unsigned int old, new, val = atomic_read(&r->refs); + unsigned int new, val = atomic_read(&r->refs); - for (;;) { + do { if (!val) return false; @@ -69,12 +69,8 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r) new = val + i; if (new < val) new = UINT_MAX; - old = atomic_cmpxchg_relaxed(&r->refs, val, new); - if (old == val) - break; - val = old; - } + } while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new)); WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); @@ -118,9 +114,9 @@ EXPORT_SYMBOL_GPL(refcount_add); */ bool refcount_inc_not_zero(refcount_t *r) { - unsigned int old, new, val = atomic_read(&r->refs); + unsigned int new, val = atomic_read(&r->refs); - for (;;) { + do { new = val + 1; if (!val) @@ -129,12 +125,7 @@ bool refcount_inc_not_zero(refcount_t *r) if (unlikely(!new)) return true; - old = atomic_cmpxchg_relaxed(&r->refs, val, new); - if (old == val) - break; - - val = old; - } + } while (!atomic_try_cmpxchg_relaxed(&r->refs, &val, new)); WARN_ONCE(new == UINT_MAX, "refcount_t: saturated; leaking memory.\n"); @@ -182,9 +173,9 @@ EXPORT_SYMBOL_GPL(refcount_inc); */ bool refcount_sub_and_test(unsigned int i, refcount_t *r) { - unsigned int old, new, val = atomic_read(&r->refs); + unsigned int new, val = atomic_read(&r->refs); - for (;;) { + do { if (unlikely(val == UINT_MAX)) return false; @@ -194,12 +185,7 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r) return false; } - old = atomic_cmpxchg_release(&r->refs, val, new); - if (old == val) - break; - - val = old; - } + } while (!atomic_try_cmpxchg_release(&r->refs, &val, new)); return !new; } @@ -258,7 +244,9 @@ EXPORT_SYMBOL_GPL(refcount_dec); */ bool refcount_dec_if_one(refcount_t *r) { - return atomic_cmpxchg_release(&r->refs, 1, 0) == 1; + int val = 1; + + return atomic_try_cmpxchg_release(&r->refs, &val, 0); } EXPORT_SYMBOL_GPL(refcount_dec_if_one); @@ -275,9 +263,9 @@ EXPORT_SYMBOL_GPL(refcount_dec_if_one); */ bool refcount_dec_not_one(refcount_t *r) { - unsigned int old, new, val = atomic_read(&r->refs); + unsigned int new, val = atomic_read(&r->refs); - for (;;) { + do { if (unlikely(val == UINT_MAX)) return true; @@ -290,12 +278,7 @@ bool refcount_dec_not_one(refcount_t *r) return true; } - old = atomic_cmpxchg_release(&r->refs, val, new); - if (old == val) - break; - - val = old; - } + } while (!atomic_try_cmpxchg_release(&r->refs, &val, new)); return true; }