Merge similar signals, and other cleanups

[simgrid.git] / src / plugins / host_energy.cpp

/* Copyright (c) 2010-2019. 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 "simgrid/plugins/energy.h"
#include "simgrid/s4u/Engine.hpp"
#include "simgrid/s4u/Exec.hpp"
#include "src/include/surf/surf.hpp"
#include "src/kernel/activity/ExecImpl.hpp"
#include "src/plugins/vm/VirtualMachineImpl.hpp"
#include "src/surf/cpu_interface.hpp"

#include <boost/algorithm/string/classification.hpp>
#include <boost/algorithm/string/split.hpp>

SIMGRID_REGISTER_PLUGIN(host_energy, "Cpu energy consumption.", &sg_host_energy_plugin_init)

/** @defgroup plugin_host_energy

This is the energy plugin, enabling to account not only for computation time, but also for the dissipated energy in the
simulated platform.
To activate this plugin, first call sg_host_energy_plugin_init() before your #MSG_init(), and then use
MSG_host_get_consumed_energy() to retrieve the consumption of a given host.

When the host is on, this energy consumption naturally depends on both the current CPU load and the host energy profile.
According to our measurements, the consumption is somehow linear in the amount of cores at full speed, with an
abnormality when all the cores are idle. The full details are in
<a href="https://hal.inria.fr/hal-01523608">our scientific paper</a> on that topic.

As a result, our energy model takes 4 parameters:

  - @b Idle: wattage (i.e., instantaneous consumption in Watt) when your host is up and running, but without anything to
do.
  - @b Epsilon: wattage when all cores are at 0 or epsilon%, but not in Idle state.
  - @b AllCores: wattage when all cores of the host are at 100%.
  - @b Off: wattage when the host is turned off.

Here is an example of XML declaration:

@code{.xml}
<host id="HostA" speed="100.0Mf" core="4">
    <prop id="wattage_per_state" value="100.0:120.0:200.0" />
    <prop id="wattage_off" value="10" />
</host>
@endcode

If the 'Epsilon' parameter is omitted in the XML declaration, 'Idle' is used instead.

This example gives the following parameters: @b Off is 10 Watts; @b Idle is 100 Watts; @b Epsilon is 120 Watts and @b
AllCores is 200 Watts.
This is enough to compute the wattage as a function of the amount of loaded cores:

<table>
<tr><th>@#Cores loaded</th><th>Wattage</th><th>Explanation</th></tr>
<tr><td>0 (idle)</td><td> 100 Watts</td><td>Idle value</td></tr>
<tr><td>0 (not idle)</td><td> 120 Watts</td><td>Epsilon value</td></tr>
<tr><td>1</td><td> 140 Watts</td><td>linear extrapolation between Epsilon and AllCores</td></tr>
<tr><td>2</td><td> 160 Watts</td><td>linear extrapolation between Epsilon and AllCores</td></tr>
<tr><td>3</td><td> 180 Watts</td><td>linear extrapolation between Epsilon and AllCores</td></tr>
<tr><td>4</td><td> 200 Watts</td><td>AllCores value</td></tr>
</table>


### How does DVFS interact with the host energy model?

If your host has several DVFS levels (several pstates), then you should give the energetic profile of each pstate level:

@code{.xml}
<host id="HostC" speed="100.0Mf,50.0Mf,20.0Mf" core="4">
    <prop id="wattage_per_state" value="95.0:120.0:200.0, 93.0:115.0:170.0, 90.0:110.0:150.0" />
    <prop id="wattage_off" value="10" />
</host>
@endcode

This encodes the following values
<table>
<tr><th>pstate</th><th>Performance</th><th>Idle</th><th>Epsilon</th><th>AllCores</th></tr>
<tr><td>0</td><td>100 Mflop/s</td><td>95 Watts</td><td>120 Watts</td><td>200 Watts</td></tr>
<tr><td>1</td><td>50 Mflop/s</td><td>93 Watts</td><td>115 Watts</td><td>170 Watts</td></tr>
<tr><td>2</td><td>20 Mflop/s</td><td>90 Watts</td><td>110 Watts</td><td>150 Watts</td></tr>
</table>

To change the pstate of a given CPU, use the following functions:
#MSG_host_get_nb_pstates(), simgrid#s4u#Host#setPstate(), #MSG_host_get_power_peak_at().

### How accurate are these models?

This model cannot be more accurate than your instantiation: with the default values, your result will not be accurate at
all. You can still get accurate energy prediction, provided that you carefully instantiate the model.
The first step is to ensure that your timing prediction match perfectly. But this is only the first step of the path,
and you really want to read <a href="https://hal.inria.fr/hal-01523608">this paper</a> to see all what you need to do
before you can get accurate energy predictions.
 */

XBT_LOG_NEW_DEFAULT_SUBCATEGORY(surf_energy, surf, "Logging specific to the SURF energy plugin");

// Forwards declaration needed to make this function a friend (because friends have external linkage by default)
static void on_simulation_end();

namespace simgrid {
namespace plugin {

class PowerRange {
public:
  double idle_;
  double epsilon_;
  double max_;
  double slope_;

  PowerRange(double idle, double epsilon, double max) : idle_(idle), epsilon_(epsilon), max_(max), slope_(max-epsilon) {}
};

class HostEnergy {
  friend void ::on_simulation_end(); // For access to host_was_used_
public:
  static simgrid::xbt::Extension<simgrid::s4u::Host, HostEnergy> EXTENSION_ID;

  explicit HostEnergy(simgrid::s4u::Host* ptr);
  ~HostEnergy();

  double get_current_watts_value();
  double get_current_watts_value(double cpu_load);
  double get_consumed_energy();
  double get_idle_consumption();
  double get_watt_min_at(int pstate);
  double get_watt_max_at(int pstate);
  double get_power_range_slope_at(int pstate);
  void update();

private:
  void init_watts_range_list();
  simgrid::s4u::Host* host_ = nullptr;
  /*< List of (idle_power, epsilon_power, max_power) tuple corresponding to each cpu pstate */
  std::vector<PowerRange> power_range_watts_list_;

  /* We need to keep track of what pstate has been used, as we will sometimes be notified only *after* a pstate has been
   * used (but we need to update the energy consumption with the old pstate!)
   */
  int pstate_           = 0;
  const int pstate_off_ = -1;

  /* Only used to split total energy into unused/used hosts.
   * If you want to get this info for something else, rather use the host_load plugin
   */
  bool host_was_used_  = false;
public:
  double watts_off_    = 0.0; /*< Consumption when the machine is turned off (shutdown) */
  double total_energy_ = 0.0; /*< Total energy consumed by the host */
  double last_updated_;       /*< Timestamp of the last energy update event*/
};

simgrid::xbt::Extension<simgrid::s4u::Host, HostEnergy> HostEnergy::EXTENSION_ID;

/* Computes the consumption so far. Called lazily on need. */
void HostEnergy::update()
{
  double start_time  = this->last_updated_;
  double finish_time = surf_get_clock();
  //
  // We may have start == finish if the past consumption was updated since the simcall was started
  // for example if 2 actors requested to update the same host's consumption in a given scheduling round.
  //
  // Even in this case, we need to save the pstate for the next call (after this if),
  // which may have changed since that recent update.
  if (start_time < finish_time) {
    double previous_energy = this->total_energy_;

    double instantaneous_power_consumption = this->get_current_watts_value();

    double energy_this_step = instantaneous_power_consumption * (finish_time - start_time);

    // TODO Trace: Trace energy_this_step from start_time to finish_time in host->getName()

    this->total_energy_ = previous_energy + energy_this_step;
    this->last_updated_ = finish_time;

    XBT_DEBUG("[update_energy of %s] period=[%.8f-%.8f]; current speed=%.2E flop/s (pstate %i); total consumption before: %.8f J -> added now: %.8f J",
              host_->get_cname(), start_time, finish_time, host_->pimpl_cpu->get_pstate_peak_speed(this->pstate_), this->pstate_, previous_energy,
              energy_this_step);
  }

  /* Save data for the upcoming time interval: whether it's on/off and the pstate if it's on */
  this->pstate_ = host_->is_on() ? host_->get_pstate() : pstate_off_;
}

HostEnergy::HostEnergy(simgrid::s4u::Host* ptr) : host_(ptr), last_updated_(surf_get_clock())
{
  init_watts_range_list();
  static bool warned = false;

  const char* off_power_str = host_->get_property("wattage_off");
  if (off_power_str == nullptr) {
    off_power_str = host_->get_property("watt_off");
    if (off_power_str != nullptr && not warned) {
      warned = true;
      XBT_WARN("Please use 'wattage_off' instead of 'watt_off' to define the idle wattage of hosts in your XML.");
    }
  }
  if (off_power_str != nullptr) {
    try {
      this->watts_off_ = std::stod(std::string(off_power_str));
    } catch (const std::invalid_argument&) {
      throw std::invalid_argument(std::string("Invalid value for property wattage_off of host ") + host_->get_cname() +
                                  ": " + off_power_str);
    }
  }
  /* watts_off is 0 by default */
}

HostEnergy::~HostEnergy() = default;

double HostEnergy::get_idle_consumption()
{
  xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
             host_->get_cname());

  return power_range_watts_list_[0].idle_;
}

double HostEnergy::get_watt_min_at(int pstate)
{
  xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
             host_->get_cname());
  return power_range_watts_list_[pstate].epsilon_;
}

double HostEnergy::get_watt_max_at(int pstate)
{
  xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
             host_->get_cname());
  return power_range_watts_list_[pstate].max_;
}

double HostEnergy::get_power_range_slope_at(int pstate)
{
    xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
               host_->get_cname());
   return power_range_watts_list_[pstate].slope_;
}

/** @brief Computes the power consumed by the host according to the current situation
 *
 * - If the host is off, that's the watts_off value
 * - if it's on, take the current pstate and the current processor load into account */
double HostEnergy::get_current_watts_value()
{
  if (this->pstate_ == pstate_off_) // The host is off (or was off at the beginning of this time interval)
    return this->watts_off_;

  double current_speed = host_->get_pstate_speed(this->pstate_);

  double cpu_load;

  if (current_speed <= 0)
    // Some users declare a pstate of speed 0 flops (e.g., to model boot time).
    // We consider that the machine is then fully loaded. That's arbitrary but it avoids a NaN
    cpu_load = 1;
  else {
    cpu_load = host_->pimpl_cpu->get_constraint()->get_usage() / current_speed;

    /* Divide by the number of cores here to have a value between 0 and 1 */
    cpu_load /= host_->pimpl_cpu->get_core_count();

    if (cpu_load > 1) // A machine with a load > 1 consumes as much as a fully loaded machine, not more
      cpu_load = 1;
    if (cpu_load > 0)
      host_was_used_ = true;
  }

  return get_current_watts_value(cpu_load);
}

/** @brief Computes the power that the host would consume at the provided processor load
 *
 * Whether the host is ON or OFF is not taken into account.
 */
double HostEnergy::get_current_watts_value(double cpu_load)
{
  xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
             host_->get_cname());

  /* Return watts_off if pstate == pstate_off (ie, if the host is off) */
  if (this->pstate_ == pstate_off_) {
    return watts_off_;
  }

  PowerRange power_range = power_range_watts_list_.at(this->pstate_);
  double current_power;

  if (cpu_load > 0)
  {
      /**
       * Something is going on, the host is not idle.
       *
       * The power consumption follows the regular model:
       * P(cpu_load) = Pstatic + Pdynamic * cpu_load
       * where Pstatic = power_range.epsilon_ and Pdynamic = power_range.slope_
       * and the cpu_load is a value between 0 and 1.
       */
      current_power = power_range.epsilon_ + cpu_load * power_range.slope_;
  }
  else
  {
      /* The host is idle, take the dedicated value! */
      current_power = power_range.idle_;
  }

  XBT_DEBUG("[get_current_watts] pstate=%i, epsilon_power=%f, max_power=%f, slope=%f", this->pstate_, power_range.epsilon_,
            power_range.max_, power_range.slope_);
  XBT_DEBUG("[get_current_watts] Current power (watts) = %f, load = %f", current_power, cpu_load);

  return current_power;
}

double HostEnergy::get_consumed_energy()
{
  if (last_updated_ < surf_get_clock()) // We need to simcall this as it modifies the environment
    simgrid::kernel::actor::simcall(std::bind(&HostEnergy::update, this));

  return total_energy_;
}

void HostEnergy::init_watts_range_list()
{
  const char* old_prop = host_->get_property("watt_per_state");
  if (old_prop != nullptr) {
    std::vector<std::string> all_power_values;
    boost::split(all_power_values, old_prop, boost::is_any_of(","));

    std::string msg = std::string("DEPRECATION WARNING: Property 'watt_per_state' will not work after v3.28.\n");
    msg += std::string("The old syntax 'Idle:OneCore:AllCores' must be converted into 'Idle:Epsilon:AllCores' to "
                       "properly model the consumption of non-whole tasks on mono-core hosts. Here are the values to "
                       "use for host '") +
           host_->get_cname() + "' in your XML file:\n";
    msg += "     <prop id=\"wattage_per_state\" value=\"";
    for (auto const& current_power_values_str : all_power_values) {
      std::vector<std::string> current_power_values;
      boost::split(current_power_values, current_power_values_str, boost::is_any_of(":"));
      double p_idle = xbt_str_parse_double((current_power_values.at(0)).c_str(),
                                           "Invalid obsolete XML file. Fix your watt_per_state property.");
      double p_one_core;
      double p_full;
      double p_epsilon;

      if (current_power_values.size() == 2) { // Case: Idle:AllCores
        p_full    = xbt_str_parse_double((current_power_values.at(1)).c_str(),
                                      "Invalid obsolete XML file. Fix your watt_per_state property.");
        p_epsilon = p_full;
      } else { // Case: Idle:Epsilon:AllCores
        p_one_core = xbt_str_parse_double((current_power_values.at(1)).c_str(),
                                          "Invalid obsolete XML file. Fix your watt_per_state property.");
        p_full     = xbt_str_parse_double((current_power_values.at(2)).c_str(),
                                      "Invalid obsolete XML file. Fix your watt_per_state property.");
        if (host_->get_core_count() == 1)
          p_epsilon = p_full;
        else
          p_epsilon = p_one_core - ((p_full - p_one_core) / (host_->get_core_count() - 1));
      }
      PowerRange range(p_idle, p_epsilon, p_full);
      power_range_watts_list_.push_back(range);

      msg += std::to_string(p_idle) + ":" + std::to_string(p_epsilon) + ":" + std::to_string(p_full);
      msg += ",";
    }
    msg.pop_back(); // Remove the extraneous ','
    msg += "\" />";
    XBT_WARN("%s", msg.c_str());
    return;
  }
  const char* all_power_values_str = host_->get_property("wattage_per_state");
  if (all_power_values_str == nullptr)
    return;

  std::vector<std::string> all_power_values;
  boost::split(all_power_values, all_power_values_str, boost::is_any_of(","));
  XBT_DEBUG("%s: power properties: %s", host_->get_cname(), all_power_values_str);

  int i = 0;
  for (auto const& current_power_values_str : all_power_values) {
    /* retrieve the power values associated with the pstate i */
    std::vector<std::string> current_power_values;
    boost::split(current_power_values, current_power_values_str, boost::is_any_of(":"));

    xbt_assert(current_power_values.size() == 2 || current_power_values.size() == 3,
               "Power properties incorrectly defined for host %s."
               "It should be 'Idle:AllCores' (or 'Idle:Epsilon:AllCores') power values.",
               host_->get_cname());

    double idle_power;
    double epsilon_power;
    double max_power;

    char* msg_idle    = bprintf("Invalid Idle value for pstate %d on host %s: %%s", i, host_->get_cname());
    char* msg_epsilon = bprintf("Invalid Epsilon value for pstate %d on host %s: %%s", i, host_->get_cname());
    char* msg_max     = bprintf("Invalid AllCores value for pstate %d on host %s: %%s", i, host_->get_cname());

    idle_power = xbt_str_parse_double((current_power_values.at(0)).c_str(), msg_idle);
    if (current_power_values.size() == 2) { // Case: Idle:AllCores
      epsilon_power = xbt_str_parse_double((current_power_values.at(0)).c_str(), msg_idle);
      max_power     = xbt_str_parse_double((current_power_values.at(1)).c_str(), msg_max);
    } else { // Case: Idle:Epsilon:AllCores
      epsilon_power = xbt_str_parse_double((current_power_values.at(1)).c_str(), msg_epsilon);
      max_power     = xbt_str_parse_double((current_power_values.at(2)).c_str(), msg_max);
    }

    XBT_DEBUG("Creating PowerRange for host %s. Idle:%f, Epsilon:%f, AllCores:%f.", host_->get_cname(), idle_power, epsilon_power, max_power);

    PowerRange range(idle_power, epsilon_power, max_power);
    power_range_watts_list_.push_back(range);
    xbt_free(msg_idle);
    xbt_free(msg_epsilon);
    xbt_free(msg_max);
    ++i;
  }
}
} // namespace plugin
} // namespace simgrid

using simgrid::plugin::HostEnergy;

/* **************************** events  callback *************************** */
static void on_creation(simgrid::s4u::Host& host)
{
  if (dynamic_cast<simgrid::s4u::VirtualMachine*>(&host)) // Ignore virtual machines
    return;

  // TODO Trace: set to zero the energy variable associated to host->getName()

  host.extension_set(new HostEnergy(&host));
}

static void on_action_state_change(simgrid::kernel::resource::CpuAction const& action,
                                   simgrid::kernel::resource::Action::State /*previous*/)
{
  for (simgrid::kernel::resource::Cpu* const& cpu : action.cpus()) {
    simgrid::s4u::Host* host = cpu->get_host();
    if (host != nullptr) {

      // If it's a VM, take the corresponding PM
      simgrid::s4u::VirtualMachine* vm = dynamic_cast<simgrid::s4u::VirtualMachine*>(host);
      if (vm) // If it's a VM, take the corresponding PM
        host = vm->get_pm();

      // Get the host_energy extension for the relevant host
      HostEnergy* host_energy = host->extension<HostEnergy>();

      if (host_energy->last_updated_ < surf_get_clock())
        host_energy->update();
    }
  }
}

/* This callback is fired either when the host changes its state (on/off) ("onStateChange") or its speed
 * (because the user changed the pstate, or because of external trace events) ("onSpeedChange") */
static void on_host_change(simgrid::s4u::Host const& host)
{
  if (dynamic_cast<simgrid::s4u::VirtualMachine const*>(&host)) // Ignore virtual machines
    return;

  HostEnergy* host_energy = host.extension<HostEnergy>();

  host_energy->update();
}

static void on_host_destruction(simgrid::s4u::Host const& host)
{
  if (dynamic_cast<simgrid::s4u::VirtualMachine const*>(&host)) // Ignore virtual machines
    return;

  XBT_INFO("Energy consumption of host %s: %f Joules", host.get_cname(),
           host.extension<HostEnergy>()->get_consumed_energy());
}

static void on_simulation_end()
{
  std::vector<simgrid::s4u::Host*> hosts = simgrid::s4u::Engine::get_instance()->get_all_hosts();

  double total_energy      = 0.0; // Total energy consumption (whole platform)
  double used_hosts_energy = 0.0; // Energy consumed by hosts that computed something
  for (size_t i = 0; i < hosts.size(); i++) {
    if (dynamic_cast<simgrid::s4u::VirtualMachine*>(hosts[i]) == nullptr) { // Ignore virtual machines

      double energy      = hosts[i]->extension<HostEnergy>()->get_consumed_energy();
      total_energy += energy;
      if (hosts[i]->extension<HostEnergy>()->host_was_used_)
        used_hosts_energy += energy;
    }
  }
  XBT_INFO("Total energy consumption: %f Joules (used hosts: %f Joules; unused/idle hosts: %f)", total_energy,
           used_hosts_energy, total_energy - used_hosts_energy);
}

/* **************************** Public interface *************************** */

/** @ingroup plugin_host_energy
 * @brief Enable host energy plugin
 * @details Enable energy plugin to get joules consumption of each cpu. Call this function before #MSG_init().
 */
void sg_host_energy_plugin_init()
{
  if (HostEnergy::EXTENSION_ID.valid())
    return;

  HostEnergy::EXTENSION_ID = simgrid::s4u::Host::extension_create<HostEnergy>();

  simgrid::s4u::Host::on_creation.connect(&on_creation);
  simgrid::s4u::Host::on_state_change.connect(&on_host_change);
  simgrid::s4u::Host::on_speed_change.connect(&on_host_change);
  simgrid::s4u::Host::on_destruction.connect(&on_host_destruction);
  simgrid::s4u::Engine::on_simulation_end.connect(&on_simulation_end);
  simgrid::kernel::resource::CpuAction::on_state_change.connect(&on_action_state_change);
  // We may only have one actor on a node. If that actor executes something like
  //   compute -> recv -> compute
  // the recv operation will not trigger a "CpuAction::on_state_change". This means
  // that the next trigger would be the 2nd compute, hence ignoring the idle time
  // during the recv call. By updating at the beginning of a compute, we can
  // fix that. (If the cpu is not idle, this is not required.)
  simgrid::s4u::Exec::on_start.connect([](simgrid::s4u::Actor const&, simgrid::s4u::Exec const& activity) {
    if (activity.get_host_number() == 1) { // We only run on one host
      simgrid::s4u::Host* host         = activity.get_host();
      simgrid::s4u::VirtualMachine* vm = dynamic_cast<simgrid::s4u::VirtualMachine*>(host);
      if (vm != nullptr)
        host = vm->get_pm();
      xbt_assert(host != nullptr);
      host->extension<HostEnergy>()->update();
    }
  });
}

/** @ingroup plugin_host_energy
 *  @brief updates the consumption of all hosts
 *
 * After this call, sg_host_get_consumed_energy() will not interrupt your process
 * (until after the next clock update).
 */
void sg_host_energy_update_all()
{
  simgrid::kernel::actor::simcall([]() {
    std::vector<simgrid::s4u::Host*> list = simgrid::s4u::Engine::get_instance()->get_all_hosts();
    for (auto const& host : list)
      if (dynamic_cast<simgrid::s4u::VirtualMachine*>(host) == nullptr) { // Ignore virtual machines
        xbt_assert(host != nullptr);
        host->extension<HostEnergy>()->update();
      }
  });
}

/** @ingroup plugin_host_energy
 *  @brief Returns the total energy consumed by the host so far (in Joules)
 *
 *  Please note that since the consumption is lazily updated, it may require a simcall to update it.
 *  The result is that the actor requesting this value will be interrupted,
 *  the value will be updated in kernel mode before returning the control to the requesting actor.
 */
double sg_host_get_consumed_energy(sg_host_t host)
{
  xbt_assert(HostEnergy::EXTENSION_ID.valid(),
             "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
  return host->extension<HostEnergy>()->get_consumed_energy();
}

/** @ingroup plugin_host_energy
 *  @brief Get the amount of watt dissipated when the host is idling
 */
double sg_host_get_idle_consumption(sg_host_t host)
{
  xbt_assert(HostEnergy::EXTENSION_ID.valid(),
             "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
  return host->extension<HostEnergy>()->get_idle_consumption();
}

/** @ingroup plugin_host_energy
 *  @brief Get the amount of watt dissipated at the given pstate when the host is idling
 */
double sg_host_get_wattmin_at(sg_host_t host, int pstate)
{
  xbt_assert(HostEnergy::EXTENSION_ID.valid(),
             "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
  return host->extension<HostEnergy>()->get_watt_min_at(pstate);
}
/** @ingroup plugin_host_energy
 *  @brief  Returns the amount of watt dissipated at the given pstate when the host burns CPU at 100%
 */
double sg_host_get_wattmax_at(sg_host_t host, int pstate)
{
  xbt_assert(HostEnergy::EXTENSION_ID.valid(),
             "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
  return host->extension<HostEnergy>()->get_watt_max_at(pstate);
}
/** @ingroup plugin_host_energy
 *  @brief  Returns the power slope at the given pstate
 */
double sg_host_get_power_range_slope_at(sg_host_t host, int pstate)
{
  xbt_assert(HostEnergy::EXTENSION_ID.valid(),
             "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
  return host->extension<HostEnergy>()->get_power_range_slope_at(pstate);
}
/** @ingroup plugin_host_energy
 *  @brief Returns the current consumption of the host
 */
double sg_host_get_current_consumption(sg_host_t host)
{
  xbt_assert(HostEnergy::EXTENSION_ID.valid(),
             "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
  return host->extension<HostEnergy>()->get_current_watts_value();
}