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stack: remove redundant orderings on pop

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The load-acquire of list->len on pop function is redundant.
Only the CAS success needs to be load-acquire.
It synchronizes with the store release in push, to ensure that the
updated head is visible when the new length is visible.
Without this, one thread in pop could see the increased length but the
old list, which doesn't have enough items yet for pop to succeed.

Signed-off-by: Steven Lariau <steven.lariau@arm.com>
Reviewed-by: Dharmik Thakkar <dharmik.thakkar@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Gage Eads <gage.eads@intel.com>
This commit is contained in:
Steven Lariau 2020-09-25 18:43:37 +01:00 committed by David Marchand
parent 9e90bc9c71
commit 2cdfe4e577
1 changed files with 2 additions and 2 deletions
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4
lib/librte_stack/rte_stack_lf_c11.h
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@ -80,7 +80,7 @@ __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
int success;
/* Reserve num elements, if available */
len = __atomic_load_n(&list->len, __ATOMIC_ACQUIRE);
len = __atomic_load_n(&list->len, __ATOMIC_RELAXED);
while (1) {
/* Does the list contain enough elements? */
@ -91,7 +91,7 @@ __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
if (__atomic_compare_exchange_n(&list->len,
&len, len - num,
1, __ATOMIC_ACQUIRE,
__ATOMIC_ACQUIRE))
__ATOMIC_RELAXED))
break;
}