From 10971638701dedadb58c88ce4d31c9375b224ed6 Mon Sep 17 00:00:00 2001 From: Vineet Gupta Date: Fri, 7 Aug 2015 13:01:39 +0530 Subject: [PATCH] ARCv2: spinlock/rwlock/atomics: reduce 1 instruction in exponential backoff The increment of delay counter was 2 instructions: Arithmatic Shfit Left (ASL) + set to 1 on overflow This can be done in 1 using ROtate Left (ROL) Suggested-by: Nigel Topham Cc: Peter Zijlstra (Intel) Cc: linux-kernel@vger.kernel.org Signed-off-by: Vineet Gupta --- arch/arc/include/asm/atomic.h | 3 +-- arch/arc/include/asm/spinlock.h | 3 +-- 2 files changed, 2 insertions(+), 4 deletions(-) diff --git a/arch/arc/include/asm/atomic.h b/arch/arc/include/asm/atomic.h index 629dfd0a0c6b..87d18ae53115 100644 --- a/arch/arc/include/asm/atomic.h +++ b/arch/arc/include/asm/atomic.h @@ -34,8 +34,7 @@ " mov %[tmp], %[delay] \n" /* tmp = delay */ \ "2: brne.d %[tmp], 0, 2b \n" /* while (tmp != 0) */ \ " sub %[tmp], %[tmp], 1 \n" /* tmp-- */ \ - " asl.f %[delay], %[delay], 1 \n" /* delay *= 2 */ \ - " mov.z %[delay], 1 \n" /* handle overflow */ \ + " rol %[delay], %[delay] \n" /* delay *= 2 */ \ " b 1b \n" /* start over */ \ "4: ; --- success --- \n" \ diff --git a/arch/arc/include/asm/spinlock.h b/arch/arc/include/asm/spinlock.h index 7071fc0da56a..db8c59d1eaeb 100644 --- a/arch/arc/include/asm/spinlock.h +++ b/arch/arc/include/asm/spinlock.h @@ -260,8 +260,7 @@ static inline void arch_write_unlock(arch_rwlock_t *rw) " mov %[tmp], %[delay] \n" /* tmp = delay */ \ "2: brne.d %[tmp], 0, 2b \n" /* while (tmp != 0) */ \ " sub %[tmp], %[tmp], 1 \n" /* tmp-- */ \ - " asl.f %[delay], %[delay], 1 \n" /* delay *= 2 */ \ - " mov.z %[delay], 1 \n" /* handle overflow */ \ + " rol %[delay], %[delay] \n" /* delay *= 2 */ \ " b 1b \n" /* start over */ \ " \n" \ "4: ; --- done --- \n" \ -- 2.20.1