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Commit e26a44a2 authored by Jan Beulich's avatar Jan Beulich Committed by Ingo Molnar
Browse files

x86: Use REP BSF unconditionally 



Make "REP BSF" unconditional, as per the suggestion of hpa
and Linus, this removes the insane BSF_PREFIX conditional
and simplifies the logic.

Suggested-by: default avatar"H. Peter Anvin" <hpa@zytor.com>
Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJan Beulich <jbeulich@suse.com>
Link: http://lkml.kernel.org/r/5058741E020000780009C014@nat28.tlf.novell.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 5870661c

arch/x86/include/asm/bitops.h

+2 −17
Original line number Diff line number Diff line
@@ -347,19 +347,6 @@ static int test_bit(int nr, const volatile unsigned long *addr); 
	 ? constant_test_bit((nr), (addr))	\

	 : variable_test_bit((nr), (addr)))



#if (defined(CONFIG_X86_GENERIC) || defined(CONFIG_GENERIC_CPU)) \

    && !defined(CONFIG_CC_OPTIMIZE_FOR_SIZE)

/*

 * Since BSF and TZCNT have sufficiently similar semantics for the purposes

 * for which we use them here, BMI-capable hardware will decode the prefixed

 * variant as 'tzcnt ...' and may execute that faster than 'bsf ...', while

 * older hardware will ignore the REP prefix and decode it as 'bsf ...'.

 */

# define BSF_PREFIX "rep;"

#else

# define BSF_PREFIX

#endif



/**

 * __ffs - find first set bit in word

 * @word: The word to search
@@ -368,7 +355,7 @@ static int test_bit(int nr, const volatile unsigned long *addr); 
 */

static inline unsigned long __ffs(unsigned long word)

{

	asm(BSF_PREFIX "bsf %1,%0"

	asm("rep; bsf %1,%0"

		: "=r" (word)

		: "rm" (word));

	return word;
@@ -382,14 +369,12 @@ static inline unsigned long __ffs(unsigned long word) 
 */

static inline unsigned long ffz(unsigned long word)

{

	asm(BSF_PREFIX "bsf %1,%0"

	asm("rep; bsf %1,%0"

		: "=r" (word)

		: "r" (~word));

	return word;

}



#undef BSF_PREFIX



/*

 * __fls: find last set bit in word

 * @word: The word to search