Generates better code (GCC-6.2.1):
0000000000000420 <ihold>:
420: 55 push %rbp
421: 8b 97 48 01 00 00 mov 0x148(%rdi),%edx
427: 48 89 e5 mov %rsp,%rbp
42a: eb 10 jmp 43c <ihold+0x1c>
42c: 89 d0 mov %edx,%eax
42e: f0 0f b1 8f 48 01 00 lock cmpxchg %ecx,0x148(%rdi)
435: 00
436: 39 c2 cmp %eax,%edx
438: 74 0d je 447 <ihold+0x27>
43a: 89 c2 mov %eax,%edx
43c: 8d 42 ff lea -0x1(%rdx),%eax
43f: 8d 4a 01 lea 0x1(%rdx),%ecx
442: 83 f8 fd cmp $0xfffffffd,%eax
445: 76 e5 jbe 42c <ihold+0xc>
447: 5d pop %rbp
448: c3 retq
0000000000001490 <ihold>:
1490: 55 push %rbp
1491: 8b 87 48 01 00 00 mov 0x148(%rdi),%eax
1497: 48 89 e5 mov %rsp,%rbp
149a: eb 0a jmp 14a6 <ihold+0x16>
149c: f0 0f b1 97 48 01 00 lock cmpxchg %edx,0x148(%rdi)
14a3: 00
14a4: 74 0b je 14b1 <ihold+0x21>
14a6: 8d 48 ff lea -0x1(%rax),%ecx
14a9: 8d 50 01 lea 0x1(%rax),%edx
14ac: 83 f9 fd cmp $0xfffffffd,%ecx
14af: 76 eb jbe 149c <ihold+0xc>
14b1: 5d pop %rbp
14b2: c3 retq
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
---
include/linux/refcount.h | 33 ++++++++++++---------------------
1 file changed, 12 insertions(+), 21 deletions(-)
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -69,7 +69,7 @@ static inline unsigned int refcount_read
static inline __refcount_check
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 (;;) {
if (!val)
@@ -81,11 +81,9 @@ bool refcount_add_not_zero(unsigned int
new = val + i;
if (new < val)
new = UINT_MAX;
- old = atomic_cmpxchg_relaxed(&r->refs, val, new);
- if (old == val)
- break;
- val = old;
+ if (atomic_try_cmpxchg_relaxed(&r->refs, &val, new))
+ break;
}
REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking
memory.\n");
@@ -108,7 +106,7 @@ static inline void refcount_add(unsigned
static inline __refcount_check
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 (;;) {
new = val + 1;
@@ -119,11 +117,8 @@ bool refcount_inc_not_zero(refcount_t *r
if (unlikely(!new))
return true;
- old = atomic_cmpxchg_relaxed(&r->refs, val, new);
- if (old == val)
+ if (atomic_try_cmpxchg_relaxed(&r->refs, &val, new))
break;
-
- val = old;
}
REFCOUNT_WARN(new == UINT_MAX, "refcount_t: saturated; leaking
memory.\n");
@@ -153,7 +148,7 @@ static inline void refcount_inc(refcount
static inline __refcount_check
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 (;;) {
if (unlikely(val == UINT_MAX))
@@ -165,11 +160,8 @@ bool refcount_sub_and_test(unsigned int
return false;
}
- old = atomic_cmpxchg_release(&r->refs, val, new);
- if (old == val)
+ if (atomic_try_cmpxchg_release(&r->refs, &val, new))
break;
-
- val = old;
}
return !new;
@@ -208,7 +200,9 @@ void refcount_dec(refcount_t *r)
static inline __refcount_check
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);
}
/*
@@ -220,7 +214,7 @@ bool refcount_dec_if_one(refcount_t *r)
static inline __refcount_check
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 (;;) {
if (unlikely(val == UINT_MAX))
@@ -235,11 +229,8 @@ bool refcount_dec_not_one(refcount_t *r)
return true;
}
- old = atomic_cmpxchg_release(&r->refs, val, new);
- if (old == val)
+ if (atomic_try_cmpxchg_release(&r->refs, &val, new))
break;
-
- val = old;
}
return true;
