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From: Gavin Hu <gavin.hu@arm.com>
To: dev@dpdk.org
Cc: thomas@monjalon.net, olivier.matz@6wind.com, chaozhu@linux.vnet.ibm.com,
bruce.richardson@intel.com, konstantin.ananyev@intel.com,
jerin.jacob@caviumnetworks.com, Honnappa.Nagarahalli@arm.com,
gavin.hu@arm.com, stable@dpdk.org
Date: Wed, 31 Oct 2018 11:35:45 +0800
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Subject: [dpdk-dev] [PATCH v2 2/2] ring: move the atomic load of head above
the loop
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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: 39368ebfc606 ("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>
Reviewed-by: Jia He <justin.he@arm.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Tested-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
---
doc/guides/rel_notes/release_18_11.rst | 7 +++++++
lib/librte_ring/rte_ring_c11_mem.h | 10 ++++------
2 files changed, 11 insertions(+), 6 deletions(-)
diff --git a/doc/guides/rel_notes/release_18_11.rst b/doc/guides/rel_notes/release_18_11.rst
index 376128f..3bbbe2a 100644
--- a/doc/guides/rel_notes/release_18_11.rst
+++ b/doc/guides/rel_notes/release_18_11.rst
@@ -158,6 +158,13 @@ New Features
* Support for runtime Rx and Tx queues setup.
* Support multicast MAC address set.
+* **Updated rte ring C11 driver.**
+
+ Updated the rte ring C11 driver including the following changes:
+
+ * Synchronize the load and store of the tail
+ * Move the atomic load of head above the loop
+
* **Added a devarg to use PCAP interface physical MAC address.**
A new devarg ``phy_mac`` was introduced to allow users to use physical
MAC address of the selected PCAP interface.
diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h
index 4851763..fdab2b9 100644
--- a/lib/librte_ring/rte_ring_c11_mem.h
+++ b/lib/librte_ring/rte_ring_c11_mem.h
@@ -60,13 +60,11 @@ __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.
*/
@@ -92,6 +90,7 @@ __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,
@@ -133,13 +132,11 @@ __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.
*/
@@ -164,6 +161,7 @@ __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,
--
2.7.4