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Commit 8989aa4a authored by Anton Blanchard's avatar Anton Blanchard Committed by Michael Ellerman
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powerpc: ppc64le optimised word at a time 

Use cmpb which compares each byte in two 64 bit values and
for each matching byte places 0xff in the target and 0x00
otherwise.

A simple hash_name microbenchmark:

http://ozlabs.org/~anton/junkcode/hash_name_bench.c



shows this version to be 10-20% faster than running the x86
version on POWER8, depending on the length.

Signed-off-by: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent fe2a1bb1

arch/powerpc/include/asm/word-at-a-time.h

+48 −15
Original line number Diff line number Diff line
@@ -42,18 +42,33 @@ static inline bool has_zero(unsigned long val, unsigned long *data, const struct 


#else



#ifdef CONFIG_64BIT



/* unused */

struct word_at_a_time {

	const unsigned long one_bits, high_bits;

};



#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }

#define WORD_AT_A_TIME_CONSTANTS { }



#ifdef CONFIG_64BIT

/* This will give us 0xff for a NULL char and 0x00 elsewhere */

static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)

{

	unsigned long ret;

	unsigned long zero = 0;



/* Alan Modra's little-endian strlen tail for 64-bit */

#define create_zero_mask(mask) (mask)

	asm("cmpb %0,%1,%2" : "=r" (ret) : "r" (a), "r" (zero));

	*bits = ret;



static inline unsigned long find_zero(unsigned long mask)

	return ret;

}



static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, const struct word_at_a_time *c)

{

	return bits;

}



/* Alan Modra's little-endian strlen tail for 64-bit */

static inline unsigned long create_zero_mask(unsigned long bits)

{

	unsigned long leading_zero_bits;

	long trailing_zero_bit_mask;
@@ -62,12 +77,30 @@ static inline unsigned long find_zero(unsigned long mask) 
	    "andc	%1,%1,%2\n\t"

	    "popcntd	%0,%1"

		: "=r" (leading_zero_bits), "=&r" (trailing_zero_bit_mask)

	     : "r" (mask));

	return leading_zero_bits >> 3;

		: "r" (bits));



	return leading_zero_bits;

}



static inline unsigned long find_zero(unsigned long mask)

{

	return mask >> 3;

}



/* This assumes that we never ask for an all 1s bitmask */

static inline unsigned long zero_bytemask(unsigned long mask)

{

	return (1UL << mask) - 1;

}



#else	/* 32-bit case */



struct word_at_a_time {

	const unsigned long one_bits, high_bits;

};



#define WORD_AT_A_TIME_CONSTANTS { REPEAT_BYTE(0x01), REPEAT_BYTE(0x80) }



/*

 * This is largely generic for little-endian machines, but the

 * optimal byte mask counting is probably going to be something
@@ -96,8 +129,6 @@ static inline unsigned long find_zero(unsigned long mask) 
	return count_masked_bytes(mask);

}



#endif



/* Return nonzero if it has a zero */

static inline unsigned long has_zero(unsigned long a, unsigned long *bits, const struct word_at_a_time *c)

{
@@ -114,7 +145,9 @@ static inline unsigned long prep_zero_mask(unsigned long a, unsigned long bits, 
/* The mask we created is directly usable as a bytemask */

#define zero_bytemask(mask) (mask)



#endif

#endif /* CONFIG_64BIT */



#endif /* __BIG_ENDIAN__ */



/*

 * We use load_unaligned_zero() in a selftest, which builds a userspace