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Commit 10971638 authored Aug 07, 2015 by Vineet Gupta

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@synopsys.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

parent 87ce6280

arch/arc/include/asm/atomic.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -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" \

arch/arc/include/asm/spinlock.h

+1 −2

Original line number	Diff line number	Diff line
		@@ -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" \