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MINOR: atomic: add a read-specific variant of __ha_cpu_relax()

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Tests on various systems show that x86 prefers not to wait at all inside
read loops while aarch64 prefers to wait a little bit. Instead of having
to stuff ifdefs around __ha_cpu_relax() inside plenty of such loops
waiting for a condition to appear, better implement a new variant that
we call __ha_cpu_relax_for_read() which honors each architecture's
preferences and is the same as __ha_cpu_relax() for other ones.
This commit is contained in:
Willy Tarreau 2024-03-15 17:31:35 +01:00
parent 5df0df96dd
commit c038ca8e8c
1 changed files with 13 additions and 0 deletions
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13
include/haproxy/atomic.h
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@ -185,6 +185,7 @@
#define __ha_barrier_full() do { } while (0)
#define __ha_compiler_barrier() do { } while (0)
#define __ha_cpu_relax() ({ 1; })
#define __ha_cpu_relax_for_read() ({ 1; })
#else /* !USE_THREAD */
@ -586,6 +587,9 @@ __ha_cas_dw(void *target, void *compare, const void *set)
/* short-lived CPU relaxation */
#define __ha_cpu_relax() ({ asm volatile("rep;nop\n"); 1; })
/* dummy relaxation: x86 prefers not to wait at all in read loops */
#define __ha_cpu_relax_for_read() ({ 1; })
#elif defined(__arm__) && (defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__))
static __inline void
@ -651,6 +655,9 @@ static __inline int __ha_cas_dw(void *target, void *compare, const void *set)
/* short-lived CPU relaxation */
#define __ha_cpu_relax() ({ asm volatile(""); 1; })
/* short wait in read loops */
#define __ha_cpu_relax_for_read() ({ asm volatile(""); 1; })
#elif defined (__aarch64__)
static __inline void
@ -697,6 +704,9 @@ __ha_barrier_atomic_full(void)
*/
#define __ha_cpu_relax() ({ asm volatile("isb" ::: "memory"); 1; })
/* aarch64 prefers to wait for real in read loops */
#define __ha_cpu_relax_for_read() ({ asm volatile("isb" ::: "memory"); 1; })
#if defined(__ARM_FEATURE_ATOMICS) && !defined(__clang__) // ARMv8.1-A atomics
/* returns 0 on failure, non-zero on success */
@ -799,6 +809,9 @@ static __inline int __ha_cas_dw(void *target, void *compare, void *set)
/* short-lived CPU relaxation */
#define __ha_cpu_relax() ({ asm volatile(""); 1; })
/* default wait in read loops */
#define __ha_cpu_relax_for_read() ({ asm volatile(""); 1; })
#endif /* end of arch-specific barrier/dwcas */
static inline void __ha_compiler_barrier(void)