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MINOR: atomic: make sure to always relax after a failed CAS

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There were a few places left where we forgot to call __ha_cpu_relax()
after a failed CAS, in the HA_ATOMIC_UPDATE_{MIN,MAX} macros, and in
a few sync_* API macros (the same as above plus HA_ATOMIC_CAS and
HA_ATOMIC_XCHG). Let's add them now.

This could have been a cause of contention, particularly with
process_stream() calling stream_update_time_stats() which uses 8 of them
in a call (4 for the server, 4 for the proxy). This may be a possible
explanation for the high CPU consumption reported in GH issue #2251.

This should be backported at least to 2.6 as it's harmless.
This commit is contained in:
Willy Tarreau 2023-08-17 08:59:15 +02:00
parent 071d689a51
commit 78fa54863d
1 changed files with 7 additions and 7 deletions
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14
include/haproxy/atomic.h
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@ -210,7 +210,7 @@
typeof(*(val)) __old_store; \
typeof((new)) __new_store = (new); \
do { __old_store = *__val_store; \
} while (!__sync_bool_compare_and_swap(__val_store, __old_store, __new_store)); \
} while (!__sync_bool_compare_and_swap(__val_store, __old_store, __new_store) && __ha_cpu_relax()); \
})
#define HA_ATOMIC_XCHG(val, new) \
@ -219,7 +219,7 @@
typeof(*(val)) __old_xchg; \
typeof((new)) __new_xchg = (new); \
do { __old_xchg = *__val_xchg; \
} while (!__sync_bool_compare_and_swap(__val_xchg, __old_xchg, __new_xchg)); \
} while (!__sync_bool_compare_and_swap(__val_xchg, __old_xchg, __new_xchg) && __ha_cpu_relax()); \
__old_xchg; \
})
@ -270,7 +270,7 @@
do { \
__oldv_cas = *__val_cas; \
__ret_cas = __sync_bool_compare_and_swap(__val_cas, *__oldp_cas, __new_cas); \
} while (!__ret_cas && *__oldp_cas == __oldv_cas); \
} while (!__ret_cas && *__oldp_cas == __oldv_cas && __ha_cpu_relax()); \
if (!__ret_cas) \
*__oldp_cas = __oldv_cas; \
__ret_cas; \
@ -286,7 +286,7 @@
typeof(*(val)) __new_max = (new); \
\
while (__old_max < __new_max && \
!HA_ATOMIC_CAS(__val, &__old_max, __new_max)); \
!HA_ATOMIC_CAS(__val, &__old_max, __new_max) && __ha_cpu_relax()); \
*__val; \
})
@ -297,7 +297,7 @@
typeof(*(val)) __new_min = (new); \
\
while (__old_min > __new_min && \
!HA_ATOMIC_CAS(__val, &__old_min, __new_min)); \
!HA_ATOMIC_CAS(__val, &__old_min, __new_min) && __ha_cpu_relax()); \
*__val; \
})
@ -405,7 +405,7 @@
typeof(*(val)) __new_max = (new); \
\
while (__old_max < __new_max && \
!HA_ATOMIC_CAS(__val, &__old_max, __new_max)); \
!HA_ATOMIC_CAS(__val, &__old_max, __new_max) && __ha_cpu_relax()); \
*__val; \
})
@ -416,7 +416,7 @@
typeof(*(val)) __new_min = (new); \
\
while (__old_min > __new_min && \
!HA_ATOMIC_CAS(__val, &__old_min, __new_min)); \
!HA_ATOMIC_CAS(__val, &__old_min, __new_min) && __ha_cpu_relax()); \
*__val; \
})