From 5f55924deaa62d6df687c131fb92aebe071ec787 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Mon, 28 Mar 2011 18:06:58 +0200 Subject: [PATCH] percpu: Avoid extra NOP in percpu_cmpxchg16b_double percpu_cmpxchg16b_double() uses alternative_io() and looks like : e8 .. .. .. .. call this_cpu_cmpxchg16b_emu X bytes NOPX or, once patched (if cpu supports native instruction) on SMP build : 65 48 0f c7 0e cmpxchg16b %gs:(%rsi) 0f 94 c0 sete %al on !SMP build : 48 0f c7 0e cmpxchg16b (%rsi) 0f 94 c0 sete %al Therefore, NOPX should be : P6_NOP3 on SMP P6_NOP2 on !SMP Signed-off-by: Eric Dumazet Acked-by: Christoph Lameter Cc: Ingo Molnar Cc: Pekka Enberg Signed-off-by: Tejun Heo --- arch/x86/include/asm/percpu.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h index d475b4398d8..d68fca61ad9 100644 --- a/arch/x86/include/asm/percpu.h +++ b/arch/x86/include/asm/percpu.h @@ -509,6 +509,11 @@ do { \ * it in software. The address used in the cmpxchg16 instruction must be * aligned to a 16 byte boundary. */ +#ifdef CONFIG_SMP +#define CMPXCHG16B_EMU_CALL "call this_cpu_cmpxchg16b_emu\n\t" P6_NOP3 +#else +#define CMPXCHG16B_EMU_CALL "call this_cpu_cmpxchg16b_emu\n\t" P6_NOP2 +#endif #define percpu_cmpxchg16b_double(pcp1, o1, o2, n1, n2) \ ({ \ char __ret; \ @@ -517,7 +522,7 @@ do { \ typeof(o2) __o2 = o2; \ typeof(o2) __n2 = n2; \ typeof(o2) __dummy; \ - alternative_io("call this_cpu_cmpxchg16b_emu\n\t" P6_NOP4, \ + alternative_io(CMPXCHG16B_EMU_CALL, \ "cmpxchg16b " __percpu_prefix "(%%rsi)\n\tsetz %0\n\t", \ X86_FEATURE_CX16, \ ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)), \ -- 2.11.4.GIT