linux-kernel - [PATCH V3 4/5] riscv: atomic: Optimize dec_if

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Message-Id: <20220420144417.2453958-5-guoren@kernel.org>
Date:   Wed, 20 Apr 2022 22:44:16 +0800
From:   guoren@...nel.org
To:     guoren@...nel.org, arnd@...db.de, palmer@...belt.com,
        mark.rutland@....com, will@...nel.org, peterz@...radead.org,
        boqun.feng@...il.com, dlustig@...dia.com, parri.andrea@...il.com
Cc:     linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, Guo Ren <guoren@...ux.alibaba.com>
Subject: [PATCH V3 4/5] riscv: atomic: Optimize dec_if_positive functions

From: Guo Ren <guoren@...ux.alibaba.com>

The arch_atomic_sub_if_positive is unnecessary for current Linux,
and it causes another register allocation. Implementing the
dec_if_positive function directly is more efficient.

Signed-off-by: Guo Ren <guoren@...ux.alibaba.com>
Signed-off-by: Guo Ren <guoren@...nel.org>
Cc: Palmer Dabbelt <palmer@...belt.com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Dan Lustig <dlustig@...dia.com>
Cc: Andrea Parri <parri.andrea@...il.com>
---
 arch/riscv/include/asm/atomic.h | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/include/asm/atomic.h b/arch/riscv/include/asm/atomic.h
index 4aaf5b01e7c6..5589e1de2c80 100644
--- a/arch/riscv/include/asm/atomic.h
+++ b/arch/riscv/include/asm/atomic.h
@@ -374,45 +374,45 @@ 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.aqrl %[rc], %[rc], %[c]\n"
 		"	bnez     %[rc], 0b\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.aqrl %[rc], %[rc], %[c]\n"
 		"	bnez     %[rc], 0b\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 */
-- 
2.25.1