Xchg on x86 implies LOCK semantics and therefore is slow. Approximate it using this_cpu_cmpxchg(). Signed-off-by: Christoph Lameter --- arch/x86/include/asm/percpu.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) Index: linux-2.6/arch/x86/include/asm/percpu.h =================================================================== --- linux-2.6.orig/arch/x86/include/asm/percpu.h 2009-12-18 15:49:09.000000000 -0600 +++ linux-2.6/arch/x86/include/asm/percpu.h 2009-12-18 15:50:12.000000000 -0600 @@ -156,6 +156,15 @@ do { \ } \ }) +#define this_cpu_xchg_x86(var, new) \ +({ __typeof(*var) __tmp_var,__tmp_old; \ + do { \ + __tmp_old = __this_cpu_read(var); \ + __tmp_var = __this_cpu_cmpxchg(var, __tmp_old, new); \ + } while (__tmp_var != __tmp_old); \ + __tmp_old; \ +}) + /* * percpu_read() makes gcc load the percpu variable every time it is * accessed while percpu_read_stable() allows the value to be cached. @@ -204,6 +213,9 @@ do { \ #define __this_cpu_cmpxchg_1(pcp, old,new) cmpxchg_local(__this_cpu_ptr(pcp), old, new) #define __this_cpu_cmpxchg_2(pcp, old,new) cmpxchg_local(__this_cpu_ptr(pcp), old, new) #define __this_cpu_cmpxchg_4(pcp, old,new) cmpxchg_local(__this_cpu_ptr(pcp), old, new) +#define __this_cpu_xchg_1(pcp, new) this_cpu_xchg_x86((pcp), new) +#define __this_cpu_xchg_2(pcp, new) this_cpu_xchg_x86((pcp), new) +#define __this_cpu_xchg_4(pcp, new) this_cpu_xchg_x86((pcp), new) #define this_cpu_read_1(pcp) percpu_from_op("mov", (pcp), "m"(pcp)) #define this_cpu_read_2(pcp) percpu_from_op("mov", (pcp), "m"(pcp)) @@ -232,6 +244,9 @@ do { \ #define this_cpu_cmpxchg_1(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) #define this_cpu_cmpxchg_2(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) #define this_cpu_cmpxchg_4(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) +#define this_cpu_xchg_1(pcp, new) this_cpu_xchg_x86((pcp), new) +#define this_cpu_xchg_2(pcp, new) this_cpu_xchg_x86((pcp), new) +#define this_cpu_xchg_4(pcp, new) this_cpu_xchg_x86((pcp), new) #define irqsafe_cpu_add_1(pcp, val) percpu_to_op("add", (pcp), val) #define irqsafe_cpu_add_2(pcp, val) percpu_to_op("add", (pcp), val) @@ -254,6 +269,9 @@ do { \ #define irqsafe_cpu_cmpxchg_1(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) #define irqsafe_cpu_cmpxchg_2(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) #define irqsafe_cpu_cmpxchg_4(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) +#define irqsafe_cpu_xchg_1(pcp, new) this_cpu_xchg_x86((pcp), new) +#define irqsafe_cpu_xchg_2(pcp, new) this_cpu_xchg_x86((pcp), new) +#define irqsafe_cpu_xchg_4(pcp, new) this_cpu_xchg_x86((pcp), new) /* * Per cpu atomic 64 bit operations are only available under 64 bit. @@ -269,6 +287,7 @@ do { \ #define __this_cpu_or_8(pcp, val) percpu_to_op("or", (pcp), val) #define __this_cpu_xor_8(pcp, val) percpu_to_op("xor", (pcp), val) #define __this_cpu_cmpxchg_8(pcp, old,new) cmpxchg_local(__this_cpu_ptr(pcp), old, new) +#define __this_cpu_xchg_8(pcp, new) this_cpu_xchg_x86((pcp), new) #define this_cpu_read_8(pcp) percpu_from_op("mov", (pcp), "m"(pcp)) #define this_cpu_write_8(pcp, val) percpu_to_op("mov", (pcp), val) @@ -279,6 +298,7 @@ do { \ #define this_cpu_or_8(pcp, val) percpu_to_op("or", (pcp), val) #define this_cpu_xor_8(pcp, val) percpu_to_op("xor", (pcp), val) #define this_cpu_cmpxchg_8(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) +#define this_cpu_xchg_8(pcp, new) this_cpu_xchg_x86((pcp), new) #define irqsafe_cpu_add_8(pcp, val) percpu_to_op("add", (pcp), val) #define irqsafe_cpu_inc_8(pcp) percpu_var_op("inc", (pcp)) @@ -287,6 +307,7 @@ do { \ #define irqsafe_cpu_or_8(pcp, val) percpu_to_op("or", (pcp), val) #define irqsafe_cpu_xor_8(pcp, val) percpu_to_op("xor", (pcp), val) #define irqsafe_cpu_cmpxchg_8(pcp, old,new) cmpxchg_local(this_cpu_ptr(pcp), old, new) +#define irqsafe_cpu_xchg_8(pcp, new) this_cpu_xchg_x86((pcp), new) #endif -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/