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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 <eric.dumazet@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Eric Dumazet 2011-03-28 18:06:58 +02:00 committed by Tejun Heo
parent 787e5b06a8
commit 5f55924dea
1 changed files with 6 additions and 1 deletions
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7
arch/x86/include/asm/percpu.h
View File

@ -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)), \