Unverified Commit 1d7f6932 authored by Guo Ren's avatar Guo Ren Committed by Palmer Dabbelt
Browse files

riscv: atomic: Optimize dec_if_positive functions 



Current implementation wastes another register to pass the
argument, but we only need addi to calculate the result. Optimize
the code with minimize the usage of registers.

Signed-off-by: default avatarGuo Ren <guoren@linux.alibaba.com>
Signed-off-by: default avatarGuo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/r/20220505035526.2974382-3-guoren@kernel.org


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent dd8437cd

arch/riscv/include/asm/atomic.h

+10 −10
Original line number Diff line number Diff line
@@ -310,47 +310,47 @@ ATOMIC_OPS() 
#undef ATOMIC_OPS

#undef ATOMIC_OP



static __always_inline int arch_atomic_sub_if_positive(atomic_t *v, int offset)

static __always_inline int arch_atomic_dec_if_positive(atomic_t *v)

{

       int prev, rc;



	__asm__ __volatile__ (

		"0:	lr.w     %[p],  %[c]\n"

		"	sub      %[rc], %[p], %[o]\n"

		"	addi     %[rc], %[p], -1\n"

		"	bltz     %[rc], 1f\n"

		"	sc.w.rl  %[rc], %[rc], %[c]\n"

		"	bnez     %[rc], 0b\n"

		"	fence    rw, rw\n"

		"1:\n"

		: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)

		: [o]"r" (offset)

		:

		: "memory");

	return prev - offset;

	return prev - 1;

}



#define arch_atomic_dec_if_positive(v)	arch_atomic_sub_if_positive(v, 1)

#define arch_atomic_dec_if_positive arch_atomic_dec_if_positive



#ifndef CONFIG_GENERIC_ATOMIC64

static __always_inline s64 arch_atomic64_sub_if_positive(atomic64_t *v, s64 offset)

static __always_inline s64 arch_atomic64_dec_if_positive(atomic64_t *v)

{

       s64 prev;

       long rc;



	__asm__ __volatile__ (

		"0:	lr.d     %[p],  %[c]\n"

		"	sub      %[rc], %[p], %[o]\n"

		"	addi      %[rc], %[p], -1\n"

		"	bltz     %[rc], 1f\n"

		"	sc.d.rl  %[rc], %[rc], %[c]\n"

		"	bnez     %[rc], 0b\n"

		"	fence    rw, rw\n"

		"1:\n"

		: [p]"=&r" (prev), [rc]"=&r" (rc), [c]"+A" (v->counter)

		: [o]"r" (offset)

		:

		: "memory");

	return prev - offset;

	return prev - 1;

}



#define arch_atomic64_dec_if_positive(v)	arch_atomic64_sub_if_positive(v, 1)

#define arch_atomic64_dec_if_positive	arch_atomic64_dec_if_positive

#endif



#endif /* _ASM_RISCV_ATOMIC_H */