Introduce arch_try_cmpxchg64 for 64-bit and 32-bit targets to improve
code using cmpxchg64. On 64-bit targets, the generated assembly improves
from:
ab: 89 c8 mov %ecx,%eax
ad: 48 89 4c 24 60 mov %rcx,0x60(%rsp)
b2: 83 e0 fd and $0xfffffffd,%eax
b5: 89 54 24 64 mov %edx,0x64(%rsp)
b9: 88 44 24 60 mov %al,0x60(%rsp)
bd: 48 89 c8 mov %rcx,%rax
c0: c6 44 24 62 f2 movb $0xf2,0x62(%rsp)
c5: 48 8b 74 24 60 mov 0x60(%rsp),%rsi
ca: f0 49 0f b1 34 24 lock cmpxchg %rsi,(%r12)
d0: 48 39 c1 cmp %rax,%rcx
d3: 75 cf jne a4 <t+0xa4>
to:
b3: 89 c2 mov %eax,%edx
b5: 48 89 44 24 60 mov %rax,0x60(%rsp)
ba: 83 e2 fd and $0xfffffffd,%edx
bd: 89 4c 24 64 mov %ecx,0x64(%rsp)
c1: 88 54 24 60 mov %dl,0x60(%rsp)
c5: c6 44 24 62 f2 movb $0xf2,0x62(%rsp)
ca: 48 8b 54 24 60 mov 0x60(%rsp),%rdx
cf: f0 48 0f b1 13 lock cmpxchg %rdx,(%rbx)
d4: 75 d5 jne ab <t+0xab>
where a move and a compare after cmpxchg is saved. The improvements
for 32-bit targets are even more noticeable, because dual-word compare
after cmpxchg8b gets eliminated.
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20220515184205.103089-3-ubizjak@gmail.com
#define arch_cmpxchg64_local(ptr, o, n) \
((__typeof__(*(ptr)))__cmpxchg64_local((ptr), (unsigned long long)(o), \
(unsigned long long)(n)))
+#define arch_try_cmpxchg64(ptr, po, n) \
+ __try_cmpxchg64((ptr), (unsigned long long *)(po), \
+ (unsigned long long)(n))
#endif
static inline u64 __cmpxchg64(volatile u64 *ptr, u64 old, u64 new)
return prev;
}
+static inline bool __try_cmpxchg64(volatile u64 *ptr, u64 *pold, u64 new)
+{
+ bool success;
+ u64 old = *pold;
+ asm volatile(LOCK_PREFIX "cmpxchg8b %[ptr]"
+ CC_SET(z)
+ : CC_OUT(z) (success),
+ [ptr] "+m" (*ptr),
+ "+A" (old)
+ : "b" ((u32)new),
+ "c" ((u32)(new >> 32))
+ : "memory");
+
+ if (unlikely(!success))
+ *pold = old;
+ return success;
+}
+
#ifndef CONFIG_X86_CMPXCHG64
/*
* Building a kernel capable running on 80386 and 80486. It may be necessary
arch_cmpxchg_local((ptr), (o), (n)); \
})
+#define arch_try_cmpxchg64(ptr, po, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ arch_try_cmpxchg((ptr), (po), (n)); \
+})
+
#define system_has_cmpxchg_double() boot_cpu_has(X86_FEATURE_CX16)
#endif /* _ASM_X86_CMPXCHG_64_H */