[slubllv4 04/16] x86: Add support for cmpxchg_double

Christoph Lameter
2011-05-06T18:07:00Z

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A simple implementation that only supports the word size and does not
have a fallback mode (would require a spinlock).

And 32 and 64 bit support for cmpxchg_double. cmpxchg double uses
the cmpxchg8b or cmpxchg16b instruction on x86 processors to compare
and swap 2 machine words. This allows lockless algorithms to move more
context information through critical sections.

Set a flag CONFIG_CMPXCHG_DOUBLE to signal the support of that feature
during kernel builds.

Signed-off-by: Christoph Lameter <cl@linux.com>

---
arch/x86/Kconfig.cpu | 3 ++
arch/x86/include/asm/cmpxchg_32.h | 46 ++++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/cmpxchg_64.h | 45 +++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/cpufeature.h | 1
4 files changed, 95 insertions(+)

Index: linux-2.6/arch/x86/include/asm/cmpxchg_64.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/cmpxchg_64.h 2011-04-13 15:19:53.000000000 -0500
+++ linux-2.6/arch/x86/include/asm/cmpxchg_64.h 2011-04-15 13:14:45.000000000 -0500
@@ -151,4 +151,49 @@ extern void __cmpxchg_wrong_size(void);
cmpxchg_local((ptr), (o), (n)); \
})

+#define cmpxchg16b(ptr, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ __typeof__(o2) __junk; \
+ __typeof__(*(ptr)) __old1 = (o1); \
+ __typeof__(o2) __old2 = (o2); \
+ __typeof__(*(ptr)) __new1 = (n1); \
+ __typeof__(o2) __new2 = (n2); \
+ asm volatile(LOCK_PREFIX_HERE "lock; cmpxchg16b (%%rsi);setz %1" \
+ : "=d"(__junk), "=a"(__ret) \
+ : "S"(ptr), "b"(__new1), "c"(__new2), \
+ "a"(__old1), "d"(__old2)); \
+ __ret; })
+
+
+#define cmpxchg16b_local(ptr, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ __typeof__(o2) __junk; \
+ __typeof__(*(ptr)) __old1 = (o1); \
+ __typeof__(o2) __old2 = (o2); \
+ __typeof__(*(ptr)) __new1 = (n1); \
+ __typeof__(o2) __new2 = (n2); \
+ asm volatile("cmpxchg16b (%%rsi)\n\t\tsetz %1\n\t" \
+ : "=d"(__junk)_, "=a"(__ret) \
+ : "S"((ptr)), "b"(__new1), "c"(__new2), \
+ "a"(__old1), "d"(__old2)); \
+ __ret; })
+
+#define cmpxchg_double(ptr, o1, o2, n1, n2) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ VM_BUG_ON((unsigned long)(ptr) % 16); \
+ cmpxchg16b((ptr), (o1), (o2), (n1), (n2)); \
+})
+
+#define cmpxchg_double_local(ptr, o1, o2, n1, n2) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 8); \
+ VM_BUG_ON((unsigned long)(ptr) % 16); \
+ cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2)); \
+})
+
+#define system_has_cmpxchg_double() cpu_has_cx16
+
#endif /* _ASM_X86_CMPXCHG_64_H */
Index: linux-2.6/arch/x86/include/asm/cmpxchg_32.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/cmpxchg_32.h 2011-04-13 15:19:53.000000000 -0500
+++ linux-2.6/arch/x86/include/asm/cmpxchg_32.h 2011-04-15 13:14:45.000000000 -0500
@@ -280,4 +280,50 @@ static inline unsigned long cmpxchg_386(

#endif

+#define cmpxchg8b(ptr, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ __typeof__(o2) __dummy; \
+ __typeof__(*(ptr)) __old1 = (o1); \
+ __typeof__(o2) __old2 = (o2); \
+ __typeof__(*(ptr)) __new1 = (n1); \
+ __typeof__(o2) __new2 = (n2); \
+ asm volatile(LOCK_PREFIX_HERE "lock; cmpxchg8b (%%esi); setz %1"\
+ : "d="(__dummy), "=a" (__ret) \
+ : "S" ((ptr)), "a" (__old1), "d"(__old2), \
+ "b" (__new1), "c" (__new2) \
+ : "memory"); \
+ __ret; })
+
+
+#define cmpxchg8b_local(ptr, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ __typeof__(o2) __dummy; \
+ __typeof__(*(ptr)) __old1 = (o1); \
+ __typeof__(o2) __old2 = (o2); \
+ __typeof__(*(ptr)) __new1 = (n1); \
+ __typeof__(o2) __new2 = (n2); \
+ asm volatile("cmpxchg8b (%%esi); tsetz %1" \
+ : "d="(__dummy), "=a"(__ret) \
+ : "S" ((ptr)), "a" (__old), "d"(__old2), \
+ "b" (__new1), "c" (__new2), \
+ : "memory"); \
+ __ret; })
+
+
+#define cmpxchg_double(ptr, o1, o2, n1, n2) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
+ VM_BUG_ON((unsigned long)(ptr) % 8); \
+ cmpxchg8b((ptr), (o1), (o2), (n1), (n2)); \
+})
+
+#define cmpxchg_double_local(ptr, o1, o2, n1, n2) \
+({ \
+ BUILD_BUG_ON(sizeof(*(ptr)) != 4); \
+ VM_BUG_ON((unsigned long)(ptr) % 8); \
+ cmpxchg16b_local((ptr), (o1), (o2), (n1), (n2)); \
+})
+
#endif /* _ASM_X86_CMPXCHG_32_H */
Index: linux-2.6/arch/x86/Kconfig.cpu
===================================================================
--- linux-2.6.orig/arch/x86/Kconfig.cpu 2011-04-13 15:19:53.000000000 -0500
+++ linux-2.6/arch/x86/Kconfig.cpu 2011-04-15 13:14:45.000000000 -0500
@@ -308,6 +308,9 @@ config X86_CMPXCHG
config CMPXCHG_LOCAL
def_bool X86_64 || (X86_32 && !M386)

+config CMPXCHG_DOUBLE
+ def_bool X86_64 || (X86_32 && !M386)
+
config X86_L1_CACHE_SHIFT
int
default "7" if MPENTIUM4 || MPSC
Index: linux-2.6/arch/x86/include/asm/cpufeature.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/cpufeature.h 2011-04-15 12:51:51.000000000 -0500
+++ linux-2.6/arch/x86/include/asm/cpufeature.h 2011-04-15 13:14:45.000000000 -0500
@@ -286,6 +286,7 @@ extern const char * const x86_power_flag
#define cpu_has_hypervisor boot_cpu_has(X86_FEATURE_HYPERVISOR)
#define cpu_has_pclmulqdq boot_cpu_has(X86_FEATURE_PCLMULQDQ)
#define cpu_has_perfctr_core boot_cpu_has(X86_FEATURE_PERFCTR_CORE)
+#define cpu_has_cx16 boot_cpu_has(X86_FEATURE_CX16)

#if defined(CONFIG_X86_INVLPG) || defined(CONFIG_X86_64)
# define cpu_has_invlpg 1