Unverified Commit 55ca8d7a authored by Xiao Wang's avatar Xiao Wang Committed by Palmer Dabbelt
Browse files

riscv: Optimize hweight API with Zbb extension 



The Hamming Weight of a number is the total number of bits set in it, so
the cpop/cpopw instruction from Zbb extension can be used to accelerate
hweight() API.

Signed-off-by: default avatarXiao Wang <xiao.w.wang@intel.com>
Reviewed-by: default avatarCharlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20231112095244.4015351-1-xiao.w.wang@intel.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent c4db7ff7

arch/riscv/include/asm/arch_hweight.h

0 → 100644
+78 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

/*

 * Based on arch/x86/include/asm/arch_hweight.h

 */



#ifndef _ASM_RISCV_HWEIGHT_H

#define _ASM_RISCV_HWEIGHT_H



#include <asm/alternative-macros.h>

#include <asm/hwcap.h>



#if (BITS_PER_LONG == 64)

#define CPOPW	"cpopw "

#elif (BITS_PER_LONG == 32)

#define CPOPW	"cpop "

#else

#error "Unexpected BITS_PER_LONG"

#endif



static __always_inline unsigned int __arch_hweight32(unsigned int w)

{

#ifdef CONFIG_RISCV_ISA_ZBB

	asm_volatile_goto(ALTERNATIVE("j %l[legacy]", "nop", 0,

				      RISCV_ISA_EXT_ZBB, 1)

			  : : : : legacy);



	asm (".option push\n"

	     ".option arch,+zbb\n"

	     CPOPW "%0, %0\n"

	     ".option pop\n"

	     : "+r" (w) : :);



	return w;



legacy:

#endif

	return __sw_hweight32(w);

}



static inline unsigned int __arch_hweight16(unsigned int w)

{

	return __arch_hweight32(w & 0xffff);

}



static inline unsigned int __arch_hweight8(unsigned int w)

{

	return __arch_hweight32(w & 0xff);

}



#if BITS_PER_LONG == 64

static __always_inline unsigned long __arch_hweight64(__u64 w)

{

# ifdef CONFIG_RISCV_ISA_ZBB

	asm_volatile_goto(ALTERNATIVE("j %l[legacy]", "nop", 0,

				      RISCV_ISA_EXT_ZBB, 1)

			  : : : : legacy);



	asm (".option push\n"

	     ".option arch,+zbb\n"

	     "cpop %0, %0\n"

	     ".option pop\n"

	     : "+r" (w) : :);



	return w;



legacy:

# endif

	return __sw_hweight64(w);

}

#else /* BITS_PER_LONG == 64 */

static inline unsigned long __arch_hweight64(__u64 w)

{

	return  __arch_hweight32((u32)w) +

		__arch_hweight32((u32)(w >> 32));

}

#endif /* !(BITS_PER_LONG == 64) */



#endif /* _ASM_RISCV_HWEIGHT_H */

arch/riscv/include/asm/bitops.h

+3 −1
Original line number Diff line number Diff line
@@ -271,7 +271,9 @@ static __always_inline int variable_fls(unsigned int x) 
#include <asm-generic/bitops/fls64.h>

#include <asm-generic/bitops/sched.h>



#include <asm-generic/bitops/hweight.h>

#include <asm/arch_hweight.h>



#include <asm-generic/bitops/const_hweight.h>



#if (BITS_PER_LONG == 64)

#define __AMO(op)	"amo" #op ".d"