diff mbox series

[v4,4/4] ring: move the atomic load of head above the loop

Message ID 1537171879-64390-4-git-send-email-gavin.hu@arm.com (mailing list archive)
State Superseded, archived
Headers
Series [v4,1/4] bus/fslmc: fix undefined reference of memsegs |

Checks

Context Check Description
ci/checkpatch success coding style OK
ci/Intel-compilation success Compilation OK

Commit Message

Gavin Hu Sept. 17, 2018, 8:11 a.m. UTC 
  In __rte_ring_move_prod_head, move the __atomic_load_n up and out of
the do {} while loop as upon failure the old_head will be updated,
another load is costly and not necessary.

This helps a little on the latency,about 1~5%.

 Test result with the patch(two cores):
 SP/SC bulk enq/dequeue (size: 8): 5.64
 MP/MC bulk enq/dequeue (size: 8): 9.58
 SP/SC bulk enq/dequeue (size: 32): 1.98
 MP/MC bulk enq/dequeue (size: 32): 2.30

Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option")
Cc: stable@dpdk.org

Signed-off-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Reviewed-by: Steve Capper <steve.capper@arm.com>
Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>
---
 lib/librte_ring/rte_ring_c11_mem.h | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

Comments

Thomas Monjalon Oct. 27, 2018, 2:21 p.m. UTC | #1 
17/09/2018 10:11, Gavin Hu:
> In __rte_ring_move_prod_head, move the __atomic_load_n up and out of
> the do {} while loop as upon failure the old_head will be updated,
> another load is costly and not necessary.
> 
> This helps a little on the latency,about 1~5%.
> 
>  Test result with the patch(two cores):
>  SP/SC bulk enq/dequeue (size: 8): 5.64
>  MP/MC bulk enq/dequeue (size: 8): 9.58
>  SP/SC bulk enq/dequeue (size: 32): 1.98
>  MP/MC bulk enq/dequeue (size: 32): 2.30
> 
> Fixes: 39368ebfc6 ("ring: introduce C11 memory model barrier option")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Gavin Hu <gavin.hu@arm.com>
> Reviewed-by: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
> Reviewed-by: Steve Capper <steve.capper@arm.com>
> Reviewed-by: Ola Liljedahl <Ola.Liljedahl@arm.com>

We are missing reviews and acknowledgements on this series.
diff mbox series

Patch

diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h
index 0eae3b3..95cc508 100644
--- a/lib/librte_ring/rte_ring_c11_mem.h
+++ b/lib/librte_ring/rte_ring_c11_mem.h
@@ -61,13 +61,11 @@  __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
 	unsigned int max = n;
 	int success;
 
+	*old_head = __atomic_load_n(&r->prod.head, __ATOMIC_ACQUIRE);
 	do {
 		/* Reset n to the initial burst count */
 		n = max;
 
-		*old_head = __atomic_load_n(&r->prod.head,
-					__ATOMIC_ACQUIRE);
-
 		/* load-acquire synchronize with store-release of ht->tail
 		 * in update_tail.
 		 */
@@ -93,6 +91,7 @@  __rte_ring_move_prod_head(struct rte_ring *r, unsigned int is_sp,
 		if (is_sp)
 			r->prod.head = *new_head, success = 1;
 		else
+			/* on failure, *old_head is updated */
 			success = __atomic_compare_exchange_n(&r->prod.head,
 					old_head, *new_head,
 					0, __ATOMIC_ACQUIRE,
@@ -134,13 +133,11 @@  __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
 	int success;
 
 	/* move cons.head atomically */
+	*old_head = __atomic_load_n(&r->cons.head, __ATOMIC_ACQUIRE);
 	do {
 		/* Restore n as it may change every loop */
 		n = max;
 
-		*old_head = __atomic_load_n(&r->cons.head,
-					__ATOMIC_ACQUIRE);
-
 		/* this load-acquire synchronize with store-release of ht->tail
 		 * in update_tail.
 		 */
@@ -165,6 +162,7 @@  __rte_ring_move_cons_head(struct rte_ring *r, int is_sc,
 		if (is_sc)
 			r->cons.head = *new_head, success = 1;
 		else
+			/* on failure, *old_head will be updated */
 			success = __atomic_compare_exchange_n(&r->cons.head,
 							old_head, *new_head,
 							0, __ATOMIC_ACQUIRE,