Re: [dpdk-dev] [PATCH] rte_ring: clarify preemptable nature of ring algorithm

[Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>]

Agree Stephen.
But rte_ring is not as basic as spinlock. IMO, existing note results in more questions than answers.

From: Stephen Hemminger <stephen@networkplumber.org>
Sent: Tuesday, May 29, 2018 9:39 PM
To: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>
Cc: Olivier Matz <olivier.matz@6wind.com>; dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] rte_ring: clarify preemptable nature of ring algorithm

Spinlock has same problem

On Tue, May 29, 2018, 1:06 AM Honnappa Nagarahalli <honnappa.nagarahalli@arm.com<mailto:honnappa.nagarahalli@arm.com>> wrote:
rte_ring implementation is not preemptable 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<mailto:honnappa.nagarahalli@arm.com>>
Reviewed-by: Gavin Hu <gavin.hu@arm.com<mailto:gavin.hu@arm.com>>
Reviewed-by: Ola Liljedahl <ola.liljedahl@arm.com<mailto:ola.liljedahl@arm.com>>
---
 lib/librte_ring/rte_ring.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/lib/librte_ring/rte_ring.h b/lib/librte_ring/rte_ring.h
index d3d3f7f..2f9c945 100644
--- a/lib/librte_ring/rte_ring.h
+++ b/lib/librte_ring/rte_ring.h
@@ -26,8 +26,13 @@
  * - 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 can block threads from completing their
+ * operation under the following circumstances.
+ * A preempted thread can block other threads (operating on the same ring)
+ * from completing their operations, only if those threads are performing
+ * the same ring operation (enqueue/dequeue) as the preempted thread.
+ * In other words, a preempted consumer thread will not block any producer
+ * threads and vice versa.
  *
  */

--
2.7.4
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