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doc: add a note for multi-process in mempool guide

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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: 449c49b93a ("mempool: support handler operations")
Cc: stable@dpdk.org

Signed-off-by: Gage Eads <gage.eads@intel.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
This commit is contained in:
Gage Eads 2019-06-20 17:07:35 -05:00 committed by Thomas Monjalon
parent 93b93beb12
commit 4ae9f32ecc
1 changed files with 8 additions and 0 deletions
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doc/guides/prog_guide/mempool_lib.rst
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@ -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
---------