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Message-ID: <1438935739-9937-1-git-send-email-vgupta@synopsys.com> Date: Fri, 7 Aug 2015 13:52:19 +0530 From: Vineet Gupta <Vineet.Gupta1@...opsys.com> To: "Peter Zijlstra (Intel)" <peterz@...radead.org> CC: Vineet Gupta <Vineet.Gupta1@...opsys.com>, <linux-kernel@...r.kernel.org> 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 <ntopham@...opsys.com> Cc: Peter Zijlstra (Intel) <peterz@...radead.org> Cc: linux-kernel@...r.kernel.org Signed-off-by: Vineet Gupta <vgupta@...opsys.com> --- 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" \ -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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