[dpdk-dev] [PATCH v6 8/8] mempool/stack: add lock-free stack mempool handler

[Gage Eads <gage.eads@intel.com>]

This commit adds support for lock-free (linked list based) stack mempool
handler.

In mempool_perf_autotest the lock-based stack outperforms the
lock-free handler for certain lcore/alloc count/free count
combinations*, however:
- For applications with preemptible pthreads, a standard (lock-based)
  stack's worst-case performance (i.e. one thread being preempted while
  holding the spinlock) is much worse than the lock-free stack's.
- Using per-thread mempool caches will largely mitigate the performance
  difference.

*Test setup: x86_64 build with default config, dual-socket Xeon E5-2699 v4,
running on isolcpus cores with a tickless scheduler. The lock-based stack's
rate_persec was 0.6x-3.5x the lock-free stack's.

Signed-off-by: Gage Eads <gage.eads@intel.com>
Reviewed-by: Olivier Matz <olivier.matz@6wind.com>
---
 doc/guides/prog_guide/env_abstraction_layer.rst | 10 ++++++++++
 doc/guides/rel_notes/release_19_05.rst          |  5 +++++
 drivers/mempool/stack/rte_mempool_stack.c       | 26 +++++++++++++++++++++++--
 3 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
index c1346363b..1a4391898 100644
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -563,6 +563,16 @@ Known Issues
 
   5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR.
 
+  Alternatively, applications can use the lock-free stack mempool handler. When
+  considering this handler, note that:
+
+  - It is currently limited to the x86_64 platform, because it uses an
+    instruction (16-byte compare-and-swap) that is not yet available on other
+    platforms.
+  - It has worse average-case performance than the non-preemptive rte_ring, but
+    software caching (e.g. the mempool cache) can mitigate this by reducing the
+    number of stack accesses.
+
 + rte_timer
 
   Running  ``rte_timer_manage()`` on a non-EAL pthread is not allowed. However, resetting/stopping the timer from a non-EAL pthread is allowed.
diff --git a/doc/guides/rel_notes/release_19_05.rst b/doc/guides/rel_notes/release_19_05.rst
index 3b115b5f6..f873984ad 100644
--- a/doc/guides/rel_notes/release_19_05.rst
+++ b/doc/guides/rel_notes/release_19_05.rst
@@ -130,6 +130,11 @@ New Features
   The library supports two stack implementations: standard (lock-based) and lock-free.
   The lock-free implementation is currently limited to x86-64 platforms.
 
+* **Added Lock-Free Stack Mempool Handler.**
+
+  Added a new lock-free stack handler, which uses the newly added stack
+  library.
+
 Removed Items
 -------------
 
diff --git a/drivers/mempool/stack/rte_mempool_stack.c b/drivers/mempool/stack/rte_mempool_stack.c
index 25ccdb9af..7e85c8d6b 100644
--- a/drivers/mempool/stack/rte_mempool_stack.c
+++ b/drivers/mempool/stack/rte_mempool_stack.c
@@ -7,7 +7,7 @@
 #include <rte_stack.h>
 
 static int
-stack_alloc(struct rte_mempool *mp)
+__stack_alloc(struct rte_mempool *mp, uint32_t flags)
 {
 	char name[RTE_STACK_NAMESIZE];
 	struct rte_stack *s;
@@ -20,7 +20,7 @@ stack_alloc(struct rte_mempool *mp)
 		return -rte_errno;
 	}
 
-	s = rte_stack_create(name, mp->size, mp->socket_id, 0);
+	s = rte_stack_create(name, mp->size, mp->socket_id, flags);
 	if (s == NULL)
 		return -rte_errno;
 
@@ -30,6 +30,18 @@ stack_alloc(struct rte_mempool *mp)
 }
 
 static int
+stack_alloc(struct rte_mempool *mp)
+{
+	return __stack_alloc(mp, 0);
+}
+
+static int
+lf_stack_alloc(struct rte_mempool *mp)
+{
+	return __stack_alloc(mp, RTE_STACK_F_LF);
+}
+
+static int
 stack_enqueue(struct rte_mempool *mp, void * const *obj_table,
 	      unsigned int n)
 {
@@ -72,4 +84,14 @@ static struct rte_mempool_ops ops_stack = {
 	.get_count = stack_get_count
 };
 
+static struct rte_mempool_ops ops_lf_stack = {
+	.name = "lf_stack",
+	.alloc = lf_stack_alloc,
+	.free = stack_free,
+	.enqueue = stack_enqueue,
+	.dequeue = stack_dequeue,
+	.get_count = stack_get_count
+};
+
 MEMPOOL_REGISTER_OPS(ops_stack);
+MEMPOOL_REGISTER_OPS(ops_lf_stack);
-- 
2.13.6