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powerpc/atomic: Follow recommendations on atomic primitive comparisons

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Both IBM and Freescale programming examples presume the cmpset operands will
favor equal, and pessimize the non-equal case instead.  Do the same for
atomic_cmpset_* and atomic_fcmpset_*.  This slightly pessimizes the failure
case, in favor of the success case.

MFC after:	3 weeks
This commit is contained in:
jhibbits 2019-09-25 01:39:58 +00:00
parent c9cf854b0a
commit 53af0efd39
1 changed files with 6 additions and 6 deletions
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12
sys/powerpc/include/atomic.h
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@ -568,7 +568,7 @@ atomic_cmpset_int(volatile u_int* p, u_int cmpval, u_int newval)
__asm __volatile (
"1:\tlwarx %0, 0, %2\n\t" /* load old value */
"cmplw %3, %0\n\t" /* compare */
"bne 2f\n\t" /* exit if not equal */
"bne- 2f\n\t" /* exit if not equal */
"stwcx. %4, 0, %2\n\t" /* attempt to store */
"bne- 1b\n\t" /* spin if failed */
"li %0, 1\n\t" /* success - retval = 1 */
@ -592,12 +592,12 @@ atomic_cmpset_long(volatile u_long* p, u_long cmpval, u_long newval)
#ifdef __powerpc64__
"1:\tldarx %0, 0, %2\n\t" /* load old value */
"cmpld %3, %0\n\t" /* compare */
"bne 2f\n\t" /* exit if not equal */
"bne- 2f\n\t" /* exit if not equal */
"stdcx. %4, 0, %2\n\t" /* attempt to store */
#else
"1:\tlwarx %0, 0, %2\n\t" /* load old value */
"cmplw %3, %0\n\t" /* compare */
"bne 2f\n\t" /* exit if not equal */
"bne- 2f\n\t" /* exit if not equal */
"stwcx. %4, 0, %2\n\t" /* attempt to store */
#endif
"bne- 1b\n\t" /* spin if failed */
@ -684,7 +684,7 @@ atomic_fcmpset_int(volatile u_int *p, u_int *cmpval, u_int newval)
__asm __volatile (
"lwarx %0, 0, %3\n\t" /* load old value */
"cmplw %4, %0\n\t" /* compare */
"bne 1f\n\t" /* exit if not equal */
"bne- 1f\n\t" /* exit if not equal */
"stwcx. %5, 0, %3\n\t" /* attempt to store */
"bne- 1f\n\t" /* exit if failed */
"li %0, 1\n\t" /* success - retval = 1 */
@ -709,12 +709,12 @@ atomic_fcmpset_long(volatile u_long *p, u_long *cmpval, u_long newval)
#ifdef __powerpc64__
"ldarx %0, 0, %3\n\t" /* load old value */
"cmpld %4, %0\n\t" /* compare */
"bne 1f\n\t" /* exit if not equal */
"bne- 1f\n\t" /* exit if not equal */
"stdcx. %5, 0, %3\n\t" /* attempt to store */
#else
"lwarx %0, 0, %3\n\t" /* load old value */
"cmplw %4, %0\n\t" /* compare */
"bne 1f\n\t" /* exit if not equal */
"bne- 1f\n\t" /* exit if not equal */
"stwcx. %5, 0, %3\n\t" /* attempt to store */
#endif
"bne- 1f\n\t" /* exit if failed */