[Plugins/LB] Add LoadBalancer class

diff --git a/src/smpi/plugins/load_balancer/LoadBalancer.cpp b/src/smpi/plugins/load_balancer/LoadBalancer.cpp
new file mode 100644 (file)
index 0000000..18c28de
--- /dev/null
+++ b/src/smpi/plugins/load_balancer/LoadBalancer.cpp
@@ -0,0 +1,100 @@
+/* Copyright (c) 2006-2018. The SimGrid Team. All rights reserved.          */
+
+/* This program is free software; you can redistribute it and/or modify it
+ * under the terms of the license (GNU LGPL) which comes with this package. */
+
+#include <algorithm>
+#include <queue>
+#include <simgrid/plugins/load.h>
+#include <simgrid/s4u.hpp>
+#include <simgrid/smpi/loadbalancer/load_balancer.hpp>
+
+XBT_LOG_NEW_DEFAULT_SUBCATEGORY(plugin_load_balancer_impl, smpi, "Logging specific to the SMPI load balancing plugin");
+
+namespace simgrid {
+namespace plugin {
+namespace loadbalancer {
+
+static std::map<simgrid::s4u::Host*, double> additional_load;
+
+static bool compare_by_avg_load(simgrid::s4u::Host* a, simgrid::s4u::Host* b)
+{
+  return sg_host_get_avg_load(a) + additional_load[a] > sg_host_get_avg_load(b) + additional_load[b];
+}
+
+LoadBalancer::LoadBalancer()
+{
+}
+
+LoadBalancer::~LoadBalancer()
+{
+}
+
+void LoadBalancer::run()
+{
+  simgrid::s4u::Engine* engine                     = simgrid::s4u::Engine::get_instance();
+  std::vector<simgrid::s4u::Host*> available_hosts = engine->get_filtered_hosts([](simgrid::s4u::Host* host) {
+    return not host->is_off();
+  });
+  xbt_assert(available_hosts.size() > 0, "No hosts available; are they all switched off?");
+  for (auto& host : available_hosts) {
+    additional_load[host] = 0;
+  }
+
+  // TODO: Account for daemon background load (-> use especially the availability file)
+
+  std::vector<simgrid::s4u::ActorPtr> all_actors =
+      engine->get_filtered_actors([](simgrid::s4u::ActorPtr actor) { return not actor->is_daemon(); });
+  for (auto& actor : all_actors) {
+    new_mapping[actor] = actor->get_host();
+  }
+  // Sort the actors, from highest to lowest load; we then just iterate over these actors
+  std::sort(all_actors.begin(), all_actors.end(), [this](simgrid::s4u::ActorPtr a, simgrid::s4u::ActorPtr b) {
+    return actor_computation[a->get_pid()] < actor_computation[b->get_pid()];
+  });
+  for (auto& actor : all_actors) {
+    XBT_INFO("Order: %li", actor->get_pid());
+  }
+  // Sort the hosts. Use a heap datastructure, because we re-insert a host
+  // that got an actor assigned in a possibly different position
+  // This is equivalent to a std::greater<Host*> implementation that uses the load to compare the two objects.
+  // --> The least loaded host will be in the first position
+  std::priority_queue</*datatype*/ simgrid::s4u::Host*, /*container*/ std::vector<simgrid::s4u::Host*>,
+                      /*comparison function*/ std::function<bool(simgrid::s4u::Host*, simgrid::s4u::Host*)>>
+      usable_hosts(compare_by_avg_load, std::move(available_hosts));
+
+  for (auto& actor : all_actors) {
+    simgrid::s4u::Host* target_host = usable_hosts.top(); // This is the host with the lowest load
+
+    if (target_host != actor->get_host() && actor->get_host()->get_actor_count() > 1) {
+      usable_hosts.pop();
+
+      assign(actor, target_host); // This updates also the load
+      usable_hosts.push(target_host);
+    }
+  }
+}
+
+void LoadBalancer::assign(simgrid::s4u::ActorPtr actor, simgrid::s4u::Host* host)
+{
+  // If an actor gets re-assigned twice, we don't want to subtract
+  // the load from the same host twice so we have to use the old value of new_mapping here
+  additional_load[new_mapping[actor]] -= 1; // actor->load();
+  additional_load[host] += 1;               // actor->load();
+  new_mapping[actor] = host;
+
+  XBT_INFO("Assigning actor %li to host %s", actor->get_pid(), host->get_cname());
+}
+
+simgrid::s4u::Host* LoadBalancer::get_mapping()
+{
+  return new_mapping[simgrid::s4u::Actor::self()];
+}
+
+void LoadBalancer::record_actor_computation(simgrid::s4u::ActorPtr actor, double load)
+{
+  actor_computation[actor->get_pid()] += load;
+}
+}
+}
+}