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ARCv2: spinlock/rwlock/atomics: reduce 1 instruction in exponential backoff

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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>
This commit is contained in:
Vineet Gupta 2015-08-07 13:01:39 +05:30
parent 87ce62802f
commit 1097163870
2 changed files with 2 additions and 4 deletions
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3
arch/arc/include/asm/atomic.h
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@ -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" \

3
arch/arc/include/asm/spinlock.h
View File

@ -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" \