From 047adc17245892198be31c54cf6658080df3dc6d Mon Sep 17 00:00:00 2001 From: Gavin Hu Date: Fri, 2 Nov 2018 19:21:28 +0800 Subject: [PATCH] ring/c11: move atomic load of head above the loop 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 Reviewed-by: Honnappa Nagarahalli Reviewed-by: Steve Capper Reviewed-by: Ola Liljedahl Reviewed-by: Jia He Acked-by: Jerin Jacob Tested-by: Jerin Jacob Acked-by: Olivier Matz --- doc/guides/rel_notes/release_18_11.rst | 10 ++++++++++ lib/librte_ring/rte_ring_c11_mem.h | 10 ++++------ 2 files changed, 14 insertions(+), 6 deletions(-) diff --git a/doc/guides/rel_notes/release_18_11.rst b/doc/guides/rel_notes/release_18_11.rst index c60879c696..cfa92b8c0d 100644 --- a/doc/guides/rel_notes/release_18_11.rst +++ b/doc/guides/rel_notes/release_18_11.rst @@ -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 diff --git a/lib/librte_ring/rte_ring_c11_mem.h b/lib/librte_ring/rte_ring_c11_mem.h index 52da95a21c..7bc74a4cb0 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, @@ -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, -- 2.20.1