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ring: clarify preemptible nature of algorithm

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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>
This commit is contained in:
Honnappa Nagarahalli 2018-07-16 23:52:44 -05:00 committed by Thomas Monjalon
parent b2a4654f08
commit 4a6e683c4c
2 changed files with 11 additions and 6 deletions
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12
doc/guides/prog_guide/env_abstraction_layer.rst
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@ -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

5
lib/librte_ring/rte_ring.h
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@ -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.
*
*/