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Commit 5f55924d authored by Eric Dumazet's avatar Eric Dumazet Committed by Tejun Heo
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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: default avatarEric Dumazet <eric.dumazet@gmail.com>
Acked-by: default avatarChristoph Lameter <cl@linux.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 787e5b06

arch/x86/include/asm/percpu.h

+6 −1
Original line number Diff line number Diff line
@@ -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)),		\