The following commit has been merged into the locking/core branch of tip:
Commit-ID: d26e46f6bf329cfcc469878709baa41d3bfc7cc3
Gitweb: https://git.kernel.org/tip/d26e46f6bf329cfcc469878709baa41d3bfc7cc3
Author: Uros Bizjak <ubizjak@xxxxxxxxx>
AuthorDate: Sun, 14 Apr 2024 18:12:43 +02:00
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Sun, 14 Apr 2024 22:40:54 +02:00
locking/atomic/x86: Introduce arch_try_cmpxchg64_local()
Introduce arch_try_cmpxchg64_local() for 64-bit and 32-bit targets
to improve code using cmpxchg64_local(). On 64-bit targets, the
generated assembly improves from:
3e28: 31 c0 xor %eax,%eax
3e2a: 4d 0f b1 7d 00 cmpxchg %r15,0x0(%r13)
3e2f: 48 85 c0 test %rax,%rax
3e32: 0f 85 9f 00 00 00 jne 3ed7 <...>
to:
3e28: 31 c0 xor %eax,%eax
3e2a: 4d 0f b1 7d 00 cmpxchg %r15,0x0(%r13)
3e2f: 0f 85 9f 00 00 00 jne 3ed4 <...>
where a TEST instruction after CMPXCHG is saved. The improvements
for 32-bit targets are even more noticeable, because double-word
compare after CMPXCHG8B gets eliminated.
Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20240414161257.49145-1-ubizjak@xxxxxxxxx
---
arch/x86/include/asm/cmpxchg_32.h | 34 ++++++++++++++++++++++++++++++-
arch/x86/include/asm/cmpxchg_64.h | 6 +++++-
2 files changed, 40 insertions(+)
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h
index 9e0d330..9dedc13 100644
--- a/arch/x86/include/asm/cmpxchg_32.h
+++ b/arch/x86/include/asm/cmpxchg_32.h
@@ -64,6 +64,11 @@ static __always_inline bool __try_cmpxchg64(volatile u64 *ptr, u64 *oldp, u64 ne
return __arch_try_cmpxchg64(ptr, oldp, new, LOCK_PREFIX);
}
+static __always_inline bool __try_cmpxchg64_local(volatile u64 *ptr, u64 *oldp, u64 new)
+{
+ return __arch_try_cmpxchg64(ptr, oldp, new,);
+}
+
#ifdef CONFIG_X86_CMPXCHG64
#define arch_cmpxchg64 __cmpxchg64
@@ -72,6 +77,8 @@ static __always_inline bool __try_cmpxchg64(volatile u64 *ptr, u64 *oldp, u64 ne
#define arch_try_cmpxchg64 __try_cmpxchg64
+#define arch_try_cmpxchg64_local __try_cmpxchg64_local
+
#else
/*
@@ -150,6 +157,33 @@ static __always_inline bool arch_try_cmpxchg64(volatile u64 *ptr, u64 *oldp, u64
}
#define arch_try_cmpxchg64 arch_try_cmpxchg64
+#define __arch_try_cmpxchg64_emu_local(_ptr, _oldp, _new) \
+({ \
+ union __u64_halves o = { .full = *(_oldp), }, \
+ n = { .full = (_new), }; \
+ bool ret; \
+ \
+ asm volatile(ALTERNATIVE("call cmpxchg8b_emu", \
+ "cmpxchg8b %[ptr]", X86_FEATURE_CX8) \
+ CC_SET(e) \
+ : CC_OUT(e) (ret), \
+ [ptr] "+m" (*(_ptr)), \
+ "+a" (o.low), "+d" (o.high) \
+ : "b" (n.low), "c" (n.high), "S" (_ptr) \
+ : "memory"); \
+ \
+ if (unlikely(!ret)) \
+ *(_oldp) = o.full; \
+ \
+ likely(ret); \
+})
+
+static __always_inline bool arch_try_cmpxchg64_local(volatile u64 *ptr, u64 *oldp, u64 new)
+{
+ return __arch_try_cmpxchg64_emu_local(ptr, oldp, new);
+}
+#define arch_try_cmpxchg64_local arch_try_cmpxchg64_local
+
#endif
#define system_has_cmpxchg64() boot_cpu_has(X86_FEATURE_CX8)
diff --git a/arch/x86/include/asm/cmpxchg_64.h b/arch/x86/include/asm/cmpxchg_64.h
index c1d6cd5..5e24130 100644
--- a/arch/x86/include/asm/cmpxchg_64.h
+++ b/arch/x86/include/asm/cmpxchg_64.h
@@ -20,6 +20,12 @@
arch_try_cmpxchg((ptr), (po), (n)); \
})
+#define arch_try_cmpxchg64_local(ptr, po, n) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ arch_try_cmpxchg_local((ptr), (po), (n)); \
+})
+
union __u128_halves {
u128 full;
struct {
|