.. todo:: add the `ready` example here
+.. _s4u_ex_execution:
+
Executions on the CPU
---------------------
|br| `examples/s4u/exec-dvfs/s4u-exec-dvfs.cpp <https://framagit.org/simgrid/simgrid/tree/master/examples/s4u/exec-dvfs/s4u-exec-dvfs.cpp>`_
|br| `examples/platforms/energy_platform.xml <https://framagit.org/simgrid/simgrid/tree/master/examples/platforms/energy_platform.xml>`_
- - **Parallel tasks:**
+ - **Parallel executions:**
These objects are convenient abstractions of parallel
- computational kernels that span over several machines.
+ computational kernels that span over several machines, such as a
+ PDGEM and the other ScaLAPACK routines.
|br| `examples/s4u/exec-ptask/s4u-exec-ptask.cpp <https://framagit.org/simgrid/simgrid/tree/master/examples/s4u/exec-ptask/s4u-exec-ptask.cpp>`_
I/O on Disks and Files
* An execution of priority 2 computes twice as fast as an execution at priority 1. */
XBT_PUBLIC void execute(double flop, double priority);
-XBT_PUBLIC void parallel_execute(int host_nb, sg_host_t* host_list, double* flops_amount, double* bytes_amount);
-XBT_PUBLIC void parallel_execute(int host_nb, sg_host_t* host_list, double* flops_amount, double* bytes_amount,
+/** Block the actor until the built parallel execution terminates
+ *
+ * \rst
+ * .. _API_s4u_parallel_execute:
+ *
+ * Parallel executions convenient abstractions of parallel computational kernels that span over several machines,
+ * such as a PDGEM and the other ScaLAPACK routines. If you are interested in the effects of such parallel kernel
+ * on the platform (e.g. to schedule them wisely), there is no need to model them in all details of their internal
+ * execution and communications. It is much more convenient to model them as a single execution activity that spans
+ * over several hosts. This is exactly what s4u's Parallel Executions are.
+ *
+ * To build such an object, you need to provide a list of hosts that are involved in the parallel kernel (the
+ * actor's own host may or may not be in this list) and specify the amount of computations that should be done by
+ * each host, using a vector of flops amount. Then, you should specify the amount of data exchanged between each
+ * hosts during the parallel kernel. For that, a matrix of values is expected.
+ *
+ * For example, if your list of hosts is ``[host0, host1]``, passing a vector ``[1000, 2000]`` as a `flops_amount`
+ * vector means that `host0` should compute 1000 flops while `host1` will compute 2000 flops. A matrix of
+ * communications' sizes of ``[0, 1, 2, 3]`` specifies the following data exchanges:
+ *
+ * +-----------+-------+------+
+ * |from \\ to | host0 | host1|
+ * +===========+=======+======+
+ * |host0 | 0 | 1 |
+ * +-----------+-------+------+
+ * |host1 | 2 | 3 |
+ * +-----------+-------+------+
+ *
+ * - From host0 to host0: 0 bytes are exchanged
+ * - From host0 to host1: 1 byte is exchanged
+ * - From host1 to host0: 2 bytes are exchanged
+ * - From host1 to host1: 3 bytes are exchanged
+ *
+ * In a parallel execution, all parts (all executions on each hosts, all communications) progress exactly at the
+ * same pace, so they all terminate at the exact same pace. If one part is slow because of a slow resource or
+ * because of contention, this slows down the parallel execution as a whole.
+ *
+ * These objects are somewhat surprising from a modeling point of view. For example, the unit of their speed is
+ * somewhere between flop/sec and byte/sec. It is **strongly advised** to only use the LV08 host model when using
+ * parallel executions. Note that you can mix regular executions and communications with parallel executions,
+ * provided that the platform model is LV08.
+ *
+ * \endrst
+ */
+
+XBT_PUBLIC void parallel_execute(int host_nb, s4u::Host* host_list, double* flops_amount, double* bytes_amount);
+/** \rst
+ * Block the actor until the built :ref:`parallel execution <API_s4u_parallel_execute>` completes, or until the timeout.
+ * \endrst*/
+XBT_PUBLIC void parallel_execute(int host_nb, s4u::Host* host_list, double* flops_amount, double* bytes_amount,
double timeout);
XBT_PUBLIC ExecPtr exec_init(double flops_amounts);
/** @brief Creates a new #msg_task_t (a parallel one....).
*
* A constructor for #msg_task_t taking six arguments and returning the corresponding object.
+ *
+ * \rst
+ * See :cpp:func:`void simgrid::s4u::this_actor::parallel_execute(int, s4u::Host*, double*, double*)` for
+ * the exact semantic of the parameters.
+ * \endrst
+ *
* @param name a name for the object. It is for user-level information and can be nullptr.
* @param host_nb the number of hosts implied in the parallel task.
* @param host_list an array of @p host_nb msg_host_t.
* @param bytes_amount an array of @p host_nb* @p host_nb doubles.
* @param data a pointer to any data may want to attach to the new object.
* It is for user-level information and can be nullptr.
- * It can be retrieved with the function @ref MSG_task_get_data.
- * @see msg_task_t
- * @return The new corresponding object.
+ * It can be retrieved with the function @ref MSG_task_get_data().
*/
msg_task_t MSG_parallel_task_create(const char *name, int host_nb, const msg_host_t * host_list,
double *flops_amount, double *bytes_amount, void *data)
