Changes between Version 19 and Version 20 of Public/User_Guide/TAMPI_NAM

Timestamp:

Apr 21, 2021, 6:04:30 PM (3 years ago)

Author:

Kevin Sala

Comment:

—

Public/User_Guide/TAMPI_NAM

@@ -48 +48 @@
 This support is based on the fence synchronization mode of the MPI RMA model.
 This mode works as follows: (1) all ranks participating in a given window have to open an access epoch on that window calling `MPI_Win_fence`, (2) they perform the desired RMA operations on the NAM window, and (3) they close the epoch with another call to `MPI_Win_fence`.
-This mode of operation can be integrated into a hybrid task-based application by instantiating a task to open the epoch on the NAM window with `MPI_Win_fence`, followed by multiple concurrent tasks that write or read data to/from the NAM window, and finally, another task to close the access epoch.
-Notice that tasks can define the corresponding dependencies on the window to ensure this order of execution, as in the following example:
+This mode of operation can be integrated into a hybrid task-based application by instantiating a task to open the epoch on the NAM window with an MPI fence, followed by multiple concurrent tasks that write or read data to/from the NAM window, and finally, another task closing the access epoch with another fence.
+Notice that tasks can define the corresponding dependencies on the window to ensure this order of execution.
+
+In order to support this taskification, the fences should be managed by the TAMPI library to perform it efficiently and safely.
+We have extended the !ParaStation MPI to provide a new non-blocking function called MPI_Win_ifence that performs that starts a fence operation on a specific window and generates an MPI request to check its completion later.
+This MPI request can be then naturally handled by the TAMPI library using the `TAMPI_Iwait` function, as shown below.
 
 {{{#!c
@@ -74 +78 @@
 }
 }}}
+
+In this example, the first task opens an access epoch on the NAM window using the new `MPI_Win_ifence`.
+This function starts a fence operation, generates an MPI request and returns immediately.
+This request is then handled by the TAMPI library through the `TAMPI_Iwait`, which bind the completion of the task to the finalization of the fence operation.
+The task can continue executing immediately without blocking and finalize its execution.
+Once the fence operation finalizes, the task will complete automatically and its successor task will become ready.
+The successors are the tasks that perform `MPI_Put` operations on the window in parallel.
+Notice that the dependencies of these tasks allow them to execute all `MPI_Put` in parallel, always after the window epoch has been opened.
+After all `MPI_Put` tasks have executed, the last task can run and close the window epoch.
 
 == Heat Benchmark ==