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ring/c11: move 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: 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>
Reviewed-by: Jia He <justin.he@arm.com>
Acked-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Tested-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
This commit is contained in:
Gavin Hu 2018-11-02 19:21:28 +08:00 committed by Thomas Monjalon
parent 9ed8770628
commit 047adc1724
2 changed files with 14 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

10
doc/guides/rel_notes/release_18_11.rst
View File

@ -69,6 +69,16 @@ New Features
checked out against that dma mask and rejected if out of range. If more than
one device has addressing limitations, the dma mask is the more restricted one.
* **Updated the C11 memory model version of ring library.**
The latency is decreased for architectures using the C11 memory model
version of the ring library.
On Cavium ThunderX2 platform, the changes decreased latency by 27~29%
and 3~15% for MPMC and SPSC cases respectively (with 2 lcores). The
real improvements may vary with the number of contending lcores and
the size of ring.
* **Added hot-unplug handle mechanism.**
``rte_dev_hotplug_handle_enable`` and ``rte_dev_hotplug_handle_disable`` are

10
lib/librte_ring/rte_ring_c11_mem.h
View File

@ -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,
@ -135,13 +134,11 @@ __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.
*/
@ -166,6 +163,7 @@ __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,