ring: clarify preemptible nature of algorithm

rte_ring implementation is not preemptible only under certain
circumstances. This clarification is helpful for data plane and
control plane communication using rte_ring.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>

diff --git a/doc/guides/prog_guide/env_abstraction_layer.rst b/doc/guides/prog_guide/env_abstraction_layer.rst
index 4c51efd..d362c92 100644 (file)
--- a/doc/guides/prog_guide/env_abstraction_layer.rst
+++ b/doc/guides/prog_guide/env_abstraction_layer.rst
@@ -449,13 +449,17 @@ Known Issues
     Bypassing this constraint may cause the 2nd pthread to spin until the 1st one is scheduled again.
     Moreover, if the 1st pthread is preempted by a context that has an higher priority, it may even cause a dead lock.
 
-  This does not mean it cannot be used, simply, there is a need to narrow down the situation when it is used by multi-pthread on the same core.
+  This means, use cases involving preemptible pthreads should consider using rte_ring carefully.
 
-  1. It CAN be used for any single-producer or single-consumer situation.
+  1. It CAN be used for preemptible single-producer and single-consumer use case.
 
-  2. It MAY be used by multi-producer/consumer pthread whose scheduling policy are all SCHED_OTHER(cfs). User SHOULD be aware of the performance penalty before using it.
+  2. It CAN be used for non-preemptible multi-producer and preemptible single-consumer use case.
 
-  3. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR.
+  3. It CAN be used for preemptible single-producer and non-preemptible multi-consumer use case.
+
+  4. It MAY be used by preemptible multi-producer and/or preemptible multi-consumer pthreads whose scheduling policy are all SCHED_OTHER(cfs), SCHED_IDLE or SCHED_BATCH. User SHOULD be aware of the performance penalty before using it.
+
+  5. It MUST not be used by multi-producer/consumer pthreads, whose scheduling policies are SCHED_FIFO or SCHED_RR.
 
 + rte_timer
 

diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
index de1a5f3..7a731d0 100644 (file)
--- a/lib/librte_ring/rte_ring.h
+++ b/lib/librte_ring/rte_ring.h
@@ -26,8 +26,9 @@
  * - Bulk dequeue.
  * - Bulk enqueue.
  *
- * Note: the ring implementation is not preemptable. A lcore must not
- * be interrupted by another task that uses the same ring.
+ * Note: the ring implementation is not preemptible. Refer to Programmer's
+ * guide/Environment Abstraction Layer/Multiple pthread/Known Issues/rte_ring
+ * for more information.
  *
  */