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[simgrid.git] / src / msg / msg_vm.c

diff --git a/src/msg/msg_vm.c b/src/msg/msg_vm.c
index 717cb22..8055867 100644 (file)
--- a/src/msg/msg_vm.c
+++ b/src/msg/msg_vm.c
@@ -1172,8 +1172,6 @@ void MSG_vm_restore(msg_vm_t vm)
 }
 
 
-
-
 /** @brief Get the physical host of a given VM.
  *  @ingroup msg_VMs
  */
@@ -1181,3 +1179,41 @@ msg_host_t MSG_vm_get_pm(msg_vm_t vm)
 {
   return simcall_vm_get_pm(vm);
 }
+
+
+/** @brief Set a CPU bound for a given VM.
+ *  @ingroup msg_VMs
+ *
+ * 1.
+ * Note that in some cases MSG_task_set_bound() may not intuitively work for VMs.
+ *
+ * For example,
+ *  On PM0, there are Task1 and VM0.
+ *  On VM0, there is Task2.
+ * Now we bound 75% to Task1@PM0 and bound 25% to Task2@VM0.
+ * Then, 
+ *  Task1@PM0 gets 50%.
+ *  Task2@VM0 gets 25%.
+ * This is NOT 75% for Task1@PM0 and 25% for Task2@VM0, respectively.
+ *
+ * This is because a VM has the dummy CPU action in the PM layer. Putting a
+ * task on the VM does not affect the bound of the dummy CPU action. The bound
+ * of the dummy CPU action is unlimited.
+ *
+ * There are some solutions for this problem. One option is to update the bound
+ * of the dummy CPU action automatically. It should be the sum of all tasks on
+ * the VM. But, this solution might be costy, because we have to scan all tasks
+ * on the VM in share_resource() or we have to trap both the start and end of
+ * task execution.
+ *
+ * The current solution is to use MSG_vm_set_bound(), which allows us to
+ * directly set the bound of the dummy CPU action.
+ *
+ *
+ * 2.
+ * Note that bound == 0 means no bound (i.e., unlimited).
+ */
+void MSG_vm_set_bound(msg_vm_t vm, double bound)
+{
+  return simcall_vm_set_bound(vm, bound);
+}