On Wed, 1 Jun 2011, H. Peter Anvin wrote:
> On 06/01/2011 07:46 AM, Christoph Lameter wrote:
> > +#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 %2; setz %1" \
> > + : "=d"(__dummy), "=a"(__ret), "m+" (*ptr)\
> > + : "a" (__old), "d"(__old2), \
> > + "b" (__new1), "c" (__new2), \
> > + : "memory"); \
> > + __ret; })
>
> Another syntax error... did you even compile-test any of your patches on
> 32 bits?
Yes. Compiled, built and I also ran a benchmark with them. cmpxchg8b_local
is not used right now.
New patch with CMPXCHG_DOUBLE always on and the typo fix.
Subject: x86: Add support for cmpxchg_double
A simple implementation that only supports the word size and does not
have a fallback mode (would require a spinlock).
Add 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 that support for double word
cmpxchg detection has been build into the kernel. Note that each subsystem
using cmpxchg_double has to implement a fall back mechanism as long as
we offer support for processors that do not implement cmpxchg_double.
Cc: tj@xxxxxxxxxx
Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
---
arch/x86/Kconfig.cpu | 3 ++
arch/x86/include/asm/cmpxchg_32.h | 48 ++++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/cmpxchg_64.h | 45 +++++++++++++++++++++++++++++++++++
arch/x86/include/asm/cpufeature.h | 2 +
4 files changed, 98 insertions(+)
Index: linux-2.6/arch/x86/include/asm/cmpxchg_64.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/cmpxchg_64.h 2011-06-01 11:01:05.002406114 -0500
+++ linux-2.6/arch/x86/include/asm/cmpxchg_64.h 2011-06-01 11:01:48.222405834 -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 "cmpxchg16b %2;setz %1" \
+ : "=d"(__junk), "=a"(__ret), "+m" (*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 %2;setz %1" \
+ : "=d"(__junk), "=a"(__ret), "+m" (*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 2011-06-01 11:01:05.022406109 -0500
+++ linux-2.6/arch/x86/include/asm/cmpxchg_32.h 2011-06-01 11:01:48.222405834 -0500
@@ -280,4 +280,52 @@ 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 "cmpxchg8b %2; setz %1" \
+ : "=d"(__dummy), "=a" (__ret), "+m" (*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 %2; setz %1" \
+ : "=d"(__dummy), "=a"(__ret), "+m" (*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)); \
+})
+
+#define system_has_cmpxchg_double() cpu_has_cx8
+
#endif /* _ASM_X86_CMPXCHG_32_H */
Index: linux-2.6/arch/x86/Kconfig.cpu
===================================================================
--- linux-2.6.orig/arch/x86/Kconfig.cpu 2011-06-01 11:01:05.032406108 -0500
+++ linux-2.6/arch/x86/Kconfig.cpu 2011-06-01 11:02:20.912405628 -0500
@@ -312,6 +312,9 @@ config X86_CMPXCHG
config CMPXCHG_LOCAL
def_bool X86_64 || (X86_32 && !M386)
+config CMPXCHG_DOUBLE
+ def_bool y
+
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 2011-06-01 11:01:05.012406112 -0500
+++ linux-2.6/arch/x86/include/asm/cpufeature.h 2011-06-01 11:01:48.222405834 -0500
@@ -288,6 +288,8 @@ 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_cx8 boot_cpu_has(X86_FEATURE_CX8)
+#define cpu_has_cx16 boot_cpu_has(X86_FEATURE_CX16)
#if defined(CONFIG_X86_INVLPG) || defined(CONFIG_X86_64)
# define cpu_has_invlpg 1
--
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