Re: [PATCH 5/6] ARCv2: spinlock/rwlock/atomics: Delayed retry of failed SCOND with exponential backoff

From: Peter Zijlstra
Date: Mon Aug 03 2015 - 07:51:11 EST


On Mon, Aug 03, 2015 at 03:33:07PM +0530, Vineet Gupta wrote:
> +#define SCOND_FAIL_RETRY_ASM \
> + " bz 4f \n" \
> + " ; --- scond fail delay --- \n" \
> + " mov %[tmp], %[delay] \n" /* tmp = delay */ \
> + "2: brne.d %[tmp], 0, 2b \n" /* while (tmp != 0) */ \
> + " sub %[tmp], %[tmp], 1 \n" /* tmp-- */ \
> + " asl %[delay], %[delay], 1 \n" /* delay *= 2 */ \
> + " b 1b \n" /* start over */ \
> + "4: ; --- success --- \n" \

One more note, you might want a test to handle the case where delay *= 2
overflows and results in a 0.
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