[v2] doc: add multi-proc shared lib mempool note
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Commit Message
The mempool library assigns handler ops indexes based on the dynamic load
order of mempool handlers. Indexes are used so a mempool can be used by
multiple processes, but this only works if all processes agree on the
mapping from index to mempool handler.
When using the '-d' argument, it's possible for different processes to load
mempool handlers in different orders, and thus have different
index->handler mappings. Using a mempool in multiple of such processes will
result in undefined behavior.
This commit adds a note to the mempool library programmer's guide warning
users against this.
Fixes: 449c49b93a6b ("mempool: support handler operations")
Cc: stable@dpdk.org
Signed-off-by: Gage Eads <gage.eads@intel.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
---
doc/guides/prog_guide/mempool_lib.rst | 8 ++++++++
1 file changed, 8 insertions(+)
v2: add another empty line
Comments
21/06/2019 00:07, Gage Eads:
> The mempool library assigns handler ops indexes based on the dynamic load
> order of mempool handlers. Indexes are used so a mempool can be used by
> multiple processes, but this only works if all processes agree on the
> mapping from index to mempool handler.
>
> When using the '-d' argument, it's possible for different processes to load
> mempool handlers in different orders, and thus have different
> index->handler mappings. Using a mempool in multiple of such processes will
> result in undefined behavior.
>
> This commit adds a note to the mempool library programmer's guide warning
> users against this.
>
> Fixes: 449c49b93a6b ("mempool: support handler operations")
> Cc: stable@dpdk.org
>
> Signed-off-by: Gage Eads <gage.eads@intel.com>
> Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Applied, thanks
@@ -133,6 +133,14 @@ For applications that use ``rte_pktmbuf_create()``, there is a config setting
(``RTE_MBUF_DEFAULT_MEMPOOL_OPS``) that allows the application to make use of
an alternative mempool handler.
+ .. note::
+
+ When running a DPDK application with shared libraries, mempool handler
+ shared objects specified with the '-d' EAL command-line parameter are
+ dynamically loaded. When running a multi-process application with shared
+ libraries, the -d arguments for mempool handlers *must be specified in the
+ same order for all processes* to ensure correct operation.
+
Use Cases
---------