path: root/doc/guides/prog_guide/multi_proc_support.rst
diff options
authorAnatoly Burakov <>2018-06-26 11:53:18 +0100
committerThomas Monjalon <>2018-07-13 12:42:05 +0200
commit3456b5ea1a1d3326c259c80ad72f1f1e08e64ea0 (patch)
tree5f201fe7c9862b55631d4b9c09b97941128dafd7 /doc/guides/prog_guide/multi_proc_support.rst
parentdaf9bfca717e6ccfe99c690cc2124bcf606bab85 (diff)
doc: add IPC callback limitations
For asynchronous requests, user callback may be triggered either from IPC thread or from interrupt thread. Because of this, delivery of other interrupt-based events such as alarms may not be possible inside the asynchronous IPC request callback handler. Document this limitation. Signed-off-by: Anatoly Burakov <>
Diffstat (limited to 'doc/guides/prog_guide/multi_proc_support.rst')
1 files changed, 15 insertions, 2 deletions
diff --git a/doc/guides/prog_guide/multi_proc_support.rst b/doc/guides/prog_guide/multi_proc_support.rst
index 46a00ec..1384fe3 100644
--- a/doc/guides/prog_guide/multi_proc_support.rst
+++ b/doc/guides/prog_guide/multi_proc_support.rst
@@ -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
@@ -280,6 +280,13 @@ 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.
@@ -311,6 +318,12 @@ supported. However, since sending messages (not requests) does not involve an
IPC thread, sending messages while processing another message or request is
+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