X-Git-Url: http://git.droids-corp.org/?a=blobdiff_plain;f=doc%2Fguides%2Fprog_guide%2Fmulti_proc_support.rst;h=a84083b96c8afdc0b062c8933403cb79d5140b70;hb=e95291f01966cbb2b7cd0985cc0edd40eda75a1d;hp=46a00ec11bf43ac01645d45e5808ec616a5feaaf;hpb=b31739328354b1f4068fc24cceb3f06434d19b74;p=dpdk.git

diff --git a/doc/guides/prog_guide/multi_proc_support.rst b/doc/guides/prog_guide/multi_proc_support.rst
index 46a00ec11b..a84083b96c 100644
--- a/doc/guides/prog_guide/multi_proc_support.rst
+++ b/doc/guides/prog_guide/multi_proc_support.rst
@@ -176,7 +176,7 @@ Some of these are documented below:
 
 *   The use of function pointers between multiple processes running based of different compiled binaries is not supported,
     since the location of a given function in one process may be different to its location in a second.
-    This prevents the librte_hash library from behaving properly as in a multi-threaded instance,
+    This prevents the librte_hash library from behaving properly as in a multi-process instance,
     since it uses a pointer to the hash function internally.
 
 To work around this issue, it is recommended that multi-process applications perform the hash calculations by directly calling
@@ -220,8 +220,8 @@ way communication mechanism, with the requester expecting a response from the
 other side.
 
 Both messages and requests will trigger a named callback on the receiver side.
-These callbacks will be called from within a dedicated IPC thread that is not
-part of EAL lcore threads.
+These callbacks will be called from within a dedicated IPC or interrupt thread
+that are not part of EAL lcore threads.
 
 Registering for incoming messages
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -263,9 +263,9 @@ To send a request, a message descriptor ``rte_mp_msg`` must be populated.
 Additionally, a ``timespec`` value must be specified as a timeout, after which
 IPC will stop waiting and return.
 
-For synchronous synchronous requests, the ``rte_mp_reply`` descriptor must also
-be created. This is where the responses will be stored. The list of fields that
-will be populated by IPC are as follows:
+For synchronous requests, the ``rte_mp_reply`` descriptor must also be created.
+This is where the responses will be stored.
+The list of fields that will be populated by IPC are as follows:
 
 * ``nb_sent`` - number indicating how many requests were sent (i.e. how many
   peer processes were active at the time of the request).
@@ -273,13 +273,20 @@ will be populated by IPC are as follows:
   those peer processes that were active at the time of request, how many have
   replied)
 * ``msgs`` - pointer to where all of the responses are stored. The order in
-  which responses appear is undefined. Whendoing sycnrhonous requests, this
+  which responses appear is undefined. When doing synchronous requests, this
   memory must be freed by the requestor after request completes!
 
 For asynchronous requests, a function pointer to the callback function must be
 provided instead. This callback will be called when the request either has timed
 out, or will have received a response to all the messages that were sent.
 
+.. warning::
+
+    When an asynchronous request times out, the callback will be called not by
+    a dedicated IPC thread, but rather from EAL interrupt thread. Because of
+    this, it may not be possible for DPDK to trigger another interrupt-based
+    event (such as an alarm) while handling asynchronous IPC callback.
+
 When the callback is called, the original request descriptor will be provided
 (so that it would be possible to determine for which sent message this is a
 callback to), along with a response descriptor like the one described above.
@@ -302,6 +309,13 @@ If a response is required, a new ``rte_mp_msg`` message descriptor must be
 constructed and sent via ``rte_mp_reply()`` function, along with ``peer``
 pointer. The resulting response will then be delivered to the correct requestor.
 
+.. warning::
+    Simply returning a value when processing a request callback will not send a
+    response to the request - it must always be explicitly sent even in case
+    of errors. Implementation of error signalling rests with the application,
+    there is no built-in way to indicate success or error for a request. Failing
+    to do so will cause the requestor to time out while waiting on a response.
+
 Misc considerations
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -311,6 +325,17 @@ supported. However, since sending messages (not requests) does not involve an
 IPC thread, sending messages while processing another message or request is
 supported.
 
+Since the memory sybsystem uses IPC internally, memory allocations and IPC must
+not be mixed: it is not safe to use IPC inside a memory-related callback, nor is
+it safe to allocate/free memory inside IPC callbacks. Attempting to do so may
+lead to a deadlock.
+
+Asynchronous request callbacks may be triggered either from IPC thread or from
+interrupt thread, depending on whether the request has timed out. It is
+therefore suggested to avoid waiting for interrupt-based events (such as alarms)
+inside asynchronous IPC request callbacks. This limitation does not apply to
+messages or synchronous requests.
+
 If callbacks spend a long time processing the incoming requests, the requestor
 might time out, so setting the right timeout value on the requestor side is
 imperative.