diff mbox series

[1/5] lib/stack: fix inconsistent weak / strong cas

Message ID 20200911152938.8019-2-steven.lariau@arm.com (mailing list archive)
State Superseded, archived
Delegated to: David Marchand
Headers
Series lib/stack: improve lockfree C11 implementation |

Checks

Context Check Description
ci/checkpatch warning coding style issues

Commit Message

Steven Lariau Sept. 11, 2020, 3:29 p.m. UTC 
  Fix cmpexchange usage of weak / strong.
The generated code is the same on x86 and ARM (there is no weak
cmpexchange), but the old usage was inconsistent.
For push and pop update size, weak is used because cmpexchange is inside
a loop.
For pop update root, strong is used even though cmpexchange is inside a
loop, because there may be a lot of operations to do in a loop iteration
(locate the new head).

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>
---
 lib/librte_stack/rte_stack_lf_c11.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Eads, Gage Sept. 21, 2020, 5:16 p.m. UTC | #1 
> -----Original Message-----
> From: Steven Lariau <steven.lariau@arm.com>
> Sent: Friday, September 11, 2020 10:30 AM
> To: Eads, Gage <gage.eads@intel.com>; Olivier Matz <olivier.matz@6wind.com>
> Cc: dev@dpdk.org; nd@arm.com; dharmik.thakkar@arm.com; Steven Lariau
> <steven.lariau@arm.com>
> Subject: [PATCH 1/5] lib/stack: fix inconsistent weak / strong cas
> 
> Fix cmpexchange usage of weak / strong.
> The generated code is the same on x86 and ARM (there is no weak
> cmpexchange), but the old usage was inconsistent.
> For push and pop update size, weak is used because cmpexchange is inside
> a loop.
> For pop update root, strong is used even though cmpexchange is inside a
> loop, because there may be a lot of operations to do in a loop iteration
> (locate the new head).
> 
> 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>

Thanks,
Gage
diff mbox series

Patch

diff --git a/lib/librte_stack/rte_stack_lf_c11.h b/lib/librte_stack/rte_stack_lf_c11.h
index 999359f08..1e0ea0bef 100644
--- a/lib/librte_stack/rte_stack_lf_c11.h
+++ b/lib/librte_stack/rte_stack_lf_c11.h
@@ -96,7 +96,7 @@  __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
 		/* len is updated on failure */
 		if (__atomic_compare_exchange_n(&list->len,
 						&len, len - num,
-						0, __ATOMIC_ACQUIRE,
+						1, __ATOMIC_ACQUIRE,
 						__ATOMIC_ACQUIRE))
 			break;
 	}
@@ -149,7 +149,7 @@  __rte_stack_lf_pop_elems(struct rte_stack_lf_list *list,
 				(rte_int128_t *)&list->head,
 				(rte_int128_t *)&old_head,
 				(rte_int128_t *)&new_head,
-				1, __ATOMIC_RELEASE,
+				0, __ATOMIC_RELEASE,
 				__ATOMIC_RELAXED);
 	} while (success == 0);