1 /* Copyright (c) 2010-2019. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #include "simgrid/plugins/energy.h"
7 #include "simgrid/s4u/Engine.hpp"
8 #include "simgrid/s4u/Exec.hpp"
9 #include "src/include/surf/surf.hpp"
10 #include "src/kernel/activity/ExecImpl.hpp"
11 #include "src/plugins/vm/VirtualMachineImpl.hpp"
12 #include "src/surf/cpu_interface.hpp"
14 #include <boost/algorithm/string/classification.hpp>
15 #include <boost/algorithm/string/split.hpp>
17 SIMGRID_REGISTER_PLUGIN(host_energy, "Cpu energy consumption.", &sg_host_energy_plugin_init)
19 /** @defgroup plugin_host_energy
22 This is the energy plugin, enabling to account not only for computation time, but also for the dissipated energy in the
24 To activate this plugin, first call :cpp:func:`sg_host_energy_plugin_init()` before your :cpp:func:`MSG_init()`, and then use
25 :cpp:func:`MSG_host_get_consumed_energy()` to retrieve the consumption of a given host.
27 When the host is on, this energy consumption naturally depends on both the current CPU load and the host energy profile.
28 According to our measurements, the consumption is somehow linear in the amount of cores at full speed, with an
29 abnormality when all the cores are idle. The full details are in `our scientific paper <https://hal.inria.fr/hal-01523608>`_
32 As a result, our energy model takes 4 parameters:
34 - ``Idle`` wattage (i.e., instantaneous consumption in Watt) when your host is up and running, but without anything to do.
35 - ``Epsilon`` wattage when all cores are at 0 or epsilon%, but not in Idle state.
36 - ``AllCores`` wattage when all cores of the host are at 100%.
37 - ``Off`` wattage when the host is turned off.
39 Here is an example of XML declaration:
43 <host id="HostA" speed="100.0Mf" core="4">
44 <prop id="wattage_per_state" value="100.0:120.0:200.0" />
45 <prop id="wattage_off" value="10" />
48 If only two values are given, ``Idle`` is used for the missing ``Epsilon`` value.
50 This example gives the following parameters: ``Off`` is 10 Watts; ``Idle`` is 100 Watts; ``Epsilon`` is 120 Watts and
51 ``AllCores`` is 200 Watts.
52 This is enough to compute the wattage as a function of the amount of loaded cores:
57 <tr><th>#Cores loaded</th><th>Wattage</th><th>Explanation</th></tr>
58 <tr><td>0 (idle)</td><td> 100 Watts </td><td> Idle value</td></tr>
59 <tr><td>0 (not idle)</td><td> 120 Watts</td><td> Epsilon value</td></tr>
60 <tr><td>1</td><td> 140 Watts</td><td> Linear extrapolation between Epsilon and AllCores</td></tr>
61 <tr><td>2</td><td> 160 Watts</td><td> Linear extrapolation between Epsilon and AllCores</td></tr>
62 <tr><td>3</td><td> 180 Watts</td><td> Linear extrapolation between Epsilon and AllCores</td></tr>
63 <tr><td>4</td><td> 200 Watts</td><td> AllCores value</td></tr>
69 <h4>How does DVFS interact with the host energy model?</h4>
71 If your host has several DVFS levels (several pstates), then you should give the energetic profile of each pstate level:
75 <host id="HostC" speed="100.0Mf,50.0Mf,20.0Mf" core="4">
76 <prop id="wattage_per_state"
77 value="95.0:120.0:200.0, 93.0:115.0:170.0, 90.0:110.0:150.0" />
78 <prop id="wattage_off" value="10" />
81 This encodes the following values:
86 <tr><th>pstate</th><th>Performance</th><th>Idle</th><th>Epsilon</th><th>AllCores</th></tr>
87 <tr><td>0</td><td>100 Mflop/s</td><td>95 Watts</td><td>120 Watts</td><td>200 Watts</td></tr>
88 <tr><td>1</td><td>50 Mflop/s</td><td>93 Watts</td><td>115 Watts</td><td>170 Watts</td></tr>
89 <tr><td>2</td><td>20 Mflop/s</td><td>90 Watts</td><td>110 Watts</td><td>150 Watts</td></tr>
92 To change the pstate of a given CPU, use the following functions:
93 :cpp:func:`MSG_host_get_nb_pstates()`, :cpp:func:`simgrid::s4u::Host::set_pstate()`, :cpp:func:`MSG_host_get_power_peak_at()`.
97 <h4>How accurate are these models?</h4>
99 This model cannot be more accurate than your instantiation: with the default values, your result will not be accurate at
100 all. You can still get accurate energy prediction, provided that you carefully instantiate the model.
101 The first step is to ensure that your timing prediction match perfectly. But this is only the first step of the path,
102 and you really want to read `this paper <https://hal.inria.fr/hal-01523608>`_ to see all what you need to do
103 before you can get accurate energy predictions.
108 XBT_LOG_NEW_DEFAULT_SUBCATEGORY(surf_energy, surf, "Logging specific to the SURF energy plugin");
110 // Forwards declaration needed to make this function a friend (because friends have external linkage by default)
111 static void on_simulation_end();
123 PowerRange(double idle, double epsilon, double max) : idle_(idle), epsilon_(epsilon), max_(max), slope_(max-epsilon) {}
127 friend void ::on_simulation_end(); // For access to host_was_used_
129 static simgrid::xbt::Extension<simgrid::s4u::Host, HostEnergy> EXTENSION_ID;
131 explicit HostEnergy(simgrid::s4u::Host* ptr);
134 double get_current_watts_value();
135 double get_current_watts_value(double cpu_load);
136 double get_consumed_energy();
137 double get_idle_consumption();
138 double get_watt_min_at(int pstate);
139 double get_watt_max_at(int pstate);
140 double get_power_range_slope_at(int pstate);
144 void init_watts_range_list();
145 simgrid::s4u::Host* host_ = nullptr;
146 /*< List of (idle_power, epsilon_power, max_power) tuple corresponding to each cpu pstate */
147 std::vector<PowerRange> power_range_watts_list_;
149 /* We need to keep track of what pstate has been used, as we will sometimes be notified only *after* a pstate has been
150 * used (but we need to update the energy consumption with the old pstate!)
153 const int pstate_off_ = -1;
155 /* Only used to split total energy into unused/used hosts.
156 * If you want to get this info for something else, rather use the host_load plugin
158 bool host_was_used_ = false;
160 double watts_off_ = 0.0; /*< Consumption when the machine is turned off (shutdown) */
161 double total_energy_ = 0.0; /*< Total energy consumed by the host */
162 double last_updated_; /*< Timestamp of the last energy update event*/
165 simgrid::xbt::Extension<simgrid::s4u::Host, HostEnergy> HostEnergy::EXTENSION_ID;
167 /* Computes the consumption so far. Called lazily on need. */
168 void HostEnergy::update()
170 double start_time = this->last_updated_;
171 double finish_time = surf_get_clock();
173 // We may have start == finish if the past consumption was updated since the simcall was started
174 // for example if 2 actors requested to update the same host's consumption in a given scheduling round.
176 // Even in this case, we need to save the pstate for the next call (after this if),
177 // which may have changed since that recent update.
178 if (start_time < finish_time) {
179 double previous_energy = this->total_energy_;
181 double instantaneous_power_consumption = this->get_current_watts_value();
183 double energy_this_step = instantaneous_power_consumption * (finish_time - start_time);
185 // TODO Trace: Trace energy_this_step from start_time to finish_time in host->getName()
187 this->total_energy_ = previous_energy + energy_this_step;
188 this->last_updated_ = finish_time;
190 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",
191 host_->get_cname(), start_time, finish_time, host_->pimpl_cpu->get_pstate_peak_speed(this->pstate_), this->pstate_, previous_energy,
195 /* Save data for the upcoming time interval: whether it's on/off and the pstate if it's on */
196 this->pstate_ = host_->is_on() ? host_->get_pstate() : pstate_off_;
199 HostEnergy::HostEnergy(simgrid::s4u::Host* ptr) : host_(ptr), last_updated_(surf_get_clock())
201 init_watts_range_list();
202 static bool warned = false;
204 const char* off_power_str = host_->get_property("wattage_off");
205 if (off_power_str == nullptr) {
206 off_power_str = host_->get_property("watt_off");
207 if (off_power_str != nullptr && not warned) {
209 XBT_WARN("Please use 'wattage_off' instead of 'watt_off' to define the idle wattage of hosts in your XML.");
212 if (off_power_str != nullptr) {
214 this->watts_off_ = std::stod(std::string(off_power_str));
215 } catch (const std::invalid_argument&) {
216 throw std::invalid_argument(std::string("Invalid value for property wattage_off of host ") + host_->get_cname() +
217 ": " + off_power_str);
220 /* watts_off is 0 by default */
223 HostEnergy::~HostEnergy() = default;
225 double HostEnergy::get_idle_consumption()
227 xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
230 return power_range_watts_list_[0].idle_;
233 double HostEnergy::get_watt_min_at(int pstate)
235 xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
237 return power_range_watts_list_[pstate].epsilon_;
240 double HostEnergy::get_watt_max_at(int pstate)
242 xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
244 return power_range_watts_list_[pstate].max_;
247 double HostEnergy::get_power_range_slope_at(int pstate)
249 xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
251 return power_range_watts_list_[pstate].slope_;
254 /** @brief Computes the power consumed by the host according to the current situation
256 * - If the host is off, that's the watts_off value
257 * - if it's on, take the current pstate and the current processor load into account */
258 double HostEnergy::get_current_watts_value()
260 if (this->pstate_ == pstate_off_) // The host is off (or was off at the beginning of this time interval)
261 return this->watts_off_;
263 double current_speed = host_->get_pstate_speed(this->pstate_);
267 if (current_speed <= 0)
268 // Some users declare a pstate of speed 0 flops (e.g., to model boot time).
269 // We consider that the machine is then fully loaded. That's arbitrary but it avoids a NaN
272 cpu_load = host_->pimpl_cpu->get_constraint()->get_usage() / current_speed;
274 /* Divide by the number of cores here to have a value between 0 and 1 */
275 cpu_load /= host_->pimpl_cpu->get_core_count();
277 if (cpu_load > 1) // This condition is true for energy_ptask on 32 bits, even if cpu_load is displayed as 1.000000
278 cpu_load = 1; // That may be an harmless rounding error?
280 host_was_used_ = true;
283 return get_current_watts_value(cpu_load);
286 /** @brief Computes the power that the host would consume at the provided processor load
288 * Whether the host is ON or OFF is not taken into account.
290 double HostEnergy::get_current_watts_value(double cpu_load)
292 xbt_assert(not power_range_watts_list_.empty(), "No power range properties specified for host %s",
295 /* Return watts_off if pstate == pstate_off (ie, if the host is off) */
296 if (this->pstate_ == pstate_off_) {
300 PowerRange power_range = power_range_watts_list_.at(this->pstate_);
301 double current_power;
306 * Something is going on, the host is not idle.
308 * The power consumption follows the regular model:
309 * P(cpu_load) = Pstatic + Pdynamic * cpu_load
310 * where Pstatic = power_range.epsilon_ and Pdynamic = power_range.slope_
311 * and the cpu_load is a value between 0 and 1.
313 current_power = power_range.epsilon_ + cpu_load * power_range.slope_;
317 /* The host is idle, take the dedicated value! */
318 current_power = power_range.idle_;
321 XBT_DEBUG("[get_current_watts] pstate=%i, epsilon_power=%f, max_power=%f, slope=%f", this->pstate_, power_range.epsilon_,
322 power_range.max_, power_range.slope_);
323 XBT_DEBUG("[get_current_watts] Current power (watts) = %f, load = %f", current_power, cpu_load);
325 return current_power;
328 double HostEnergy::get_consumed_energy()
330 if (last_updated_ < surf_get_clock()) // We need to simcall this as it modifies the environment
331 simgrid::kernel::actor::simcall(std::bind(&HostEnergy::update, this));
333 return total_energy_;
336 void HostEnergy::init_watts_range_list()
338 const char* old_prop = host_->get_property("watt_per_state");
339 if (old_prop != nullptr) {
340 std::vector<std::string> all_power_values;
341 boost::split(all_power_values, old_prop, boost::is_any_of(","));
343 // XBT_ATTRIB_DEPRECATED_v327: puting this macro name here so that we find it during the deprecation cleanups of v3.28
344 std::string msg = std::string("DEPRECATION WARNING: Property 'watt_per_state' will only work until v3.28.\n");
345 msg += std::string("The old syntax 'Idle:OneCore:AllCores' must be converted into 'Idle:Epsilon:AllCores' to "
346 "properly model the consumption of non-whole tasks on mono-core hosts. Here are the values to "
348 host_->get_cname() + "' in your XML file:\n";
349 msg += " <prop id=\"wattage_per_state\" value=\"";
350 for (auto const& current_power_values_str : all_power_values) {
351 std::vector<std::string> current_power_values;
352 boost::split(current_power_values, current_power_values_str, boost::is_any_of(":"));
353 double p_idle = xbt_str_parse_double((current_power_values.at(0)).c_str(),
354 "Invalid obsolete XML file. Fix your watt_per_state property.");
359 if (current_power_values.size() == 3) {
360 p_one_core = xbt_str_parse_double((current_power_values.at(1)).c_str(),
361 "Invalid obsolete XML file. Fix your watt_per_state property.");
362 p_full = xbt_str_parse_double((current_power_values.at(2)).c_str(),
363 "Invalid obsolete XML file. Fix your watt_per_state property.");
364 if (host_->get_core_count() == 1) {
367 p_epsilon = p_one_core - ((p_full - p_one_core) / (host_->get_core_count() - 1));
369 } else { // consuption given with idle and full only
370 p_full = xbt_str_parse_double((current_power_values.at(1)).c_str(),
371 "Invalid obsolete XML file. Fix your watt_per_state property.");
372 if (host_->get_core_count() == 1) {
379 PowerRange range(p_idle, p_epsilon, p_full);
380 power_range_watts_list_.push_back(range);
382 msg += std::to_string(p_idle) + ":" + std::to_string(p_epsilon) + ":" + std::to_string(p_full);
385 msg.pop_back(); // Remove the extraneous ','
387 XBT_WARN("%s", msg.c_str());
390 const char* all_power_values_str = host_->get_property("wattage_per_state");
391 if (all_power_values_str == nullptr)
394 std::vector<std::string> all_power_values;
395 boost::split(all_power_values, all_power_values_str, boost::is_any_of(","));
396 XBT_DEBUG("%s: power properties: %s", host_->get_cname(), all_power_values_str);
399 for (auto const& current_power_values_str : all_power_values) {
400 /* retrieve the power values associated with the pstate i */
401 std::vector<std::string> current_power_values;
402 boost::split(current_power_values, current_power_values_str, boost::is_any_of(":"));
404 xbt_assert(current_power_values.size() == 2 || current_power_values.size() == 3,
405 "Power properties incorrectly defined for host %s."
406 "It should be 'Idle:AllCores' (or 'Idle:Epsilon:AllCores') power values.",
410 double epsilon_power;
413 char* msg_idle = bprintf("Invalid Idle value for pstate %d on host %s: %%s", i, host_->get_cname());
414 char* msg_epsilon = bprintf("Invalid Epsilon value for pstate %d on host %s: %%s", i, host_->get_cname());
415 char* msg_max = bprintf("Invalid AllCores value for pstate %d on host %s: %%s", i, host_->get_cname());
417 idle_power = xbt_str_parse_double((current_power_values.at(0)).c_str(), msg_idle);
418 if (current_power_values.size() == 2) { // Case: Idle:AllCores
419 epsilon_power = xbt_str_parse_double((current_power_values.at(0)).c_str(), msg_idle);
420 max_power = xbt_str_parse_double((current_power_values.at(1)).c_str(), msg_max);
421 } else { // Case: Idle:Epsilon:AllCores
422 epsilon_power = xbt_str_parse_double((current_power_values.at(1)).c_str(), msg_epsilon);
423 max_power = xbt_str_parse_double((current_power_values.at(2)).c_str(), msg_max);
426 XBT_DEBUG("Creating PowerRange for host %s. Idle:%f, Epsilon:%f, AllCores:%f.", host_->get_cname(), idle_power, epsilon_power, max_power);
428 PowerRange range(idle_power, epsilon_power, max_power);
429 power_range_watts_list_.push_back(range);
431 xbt_free(msg_epsilon);
436 } // namespace plugin
437 } // namespace simgrid
439 using simgrid::plugin::HostEnergy;
441 /* **************************** events callback *************************** */
442 static void on_creation(simgrid::s4u::Host& host)
444 if (dynamic_cast<simgrid::s4u::VirtualMachine*>(&host)) // Ignore virtual machines
447 // TODO Trace: set to zero the energy variable associated to host->getName()
449 host.extension_set(new HostEnergy(&host));
452 static void on_action_state_change(simgrid::kernel::resource::CpuAction const& action,
453 simgrid::kernel::resource::Action::State /*previous*/)
455 for (simgrid::kernel::resource::Cpu* const& cpu : action.cpus()) {
456 simgrid::s4u::Host* host = cpu->get_host();
457 if (host != nullptr) {
459 // If it's a VM, take the corresponding PM
460 simgrid::s4u::VirtualMachine* vm = dynamic_cast<simgrid::s4u::VirtualMachine*>(host);
461 if (vm) // If it's a VM, take the corresponding PM
464 // Get the host_energy extension for the relevant host
465 HostEnergy* host_energy = host->extension<HostEnergy>();
467 if (host_energy->last_updated_ < surf_get_clock())
468 host_energy->update();
473 /* This callback is fired either when the host changes its state (on/off) ("onStateChange") or its speed
474 * (because the user changed the pstate, or because of external trace events) ("onSpeedChange") */
475 static void on_host_change(simgrid::s4u::Host const& host)
477 if (dynamic_cast<simgrid::s4u::VirtualMachine const*>(&host)) // Ignore virtual machines
480 HostEnergy* host_energy = host.extension<HostEnergy>();
482 host_energy->update();
485 static void on_host_destruction(simgrid::s4u::Host const& host)
487 if (dynamic_cast<simgrid::s4u::VirtualMachine const*>(&host)) // Ignore virtual machines
490 XBT_INFO("Energy consumption of host %s: %f Joules", host.get_cname(),
491 host.extension<HostEnergy>()->get_consumed_energy());
494 static void on_simulation_end()
496 std::vector<simgrid::s4u::Host*> hosts = simgrid::s4u::Engine::get_instance()->get_all_hosts();
498 double total_energy = 0.0; // Total energy consumption (whole platform)
499 double used_hosts_energy = 0.0; // Energy consumed by hosts that computed something
500 for (size_t i = 0; i < hosts.size(); i++) {
501 if (dynamic_cast<simgrid::s4u::VirtualMachine*>(hosts[i]) == nullptr) { // Ignore virtual machines
503 double energy = hosts[i]->extension<HostEnergy>()->get_consumed_energy();
504 total_energy += energy;
505 if (hosts[i]->extension<HostEnergy>()->host_was_used_)
506 used_hosts_energy += energy;
509 XBT_INFO("Total energy consumption: %f Joules (used hosts: %f Joules; unused/idle hosts: %f)", total_energy,
510 used_hosts_energy, total_energy - used_hosts_energy);
513 /* **************************** Public interface *************************** */
515 /** @ingroup plugin_host_energy
516 * @brief Enable host energy plugin
517 * @details Enable energy plugin to get joules consumption of each cpu. Call this function before #MSG_init().
519 void sg_host_energy_plugin_init()
521 if (HostEnergy::EXTENSION_ID.valid())
524 HostEnergy::EXTENSION_ID = simgrid::s4u::Host::extension_create<HostEnergy>();
526 simgrid::s4u::Host::on_creation.connect(&on_creation);
527 simgrid::s4u::Host::on_state_change.connect(&on_host_change);
528 simgrid::s4u::Host::on_speed_change.connect(&on_host_change);
529 simgrid::s4u::Host::on_destruction.connect(&on_host_destruction);
530 simgrid::s4u::Engine::on_simulation_end.connect(&on_simulation_end);
531 simgrid::kernel::resource::CpuAction::on_state_change.connect(&on_action_state_change);
532 // We may only have one actor on a node. If that actor executes something like
533 // compute -> recv -> compute
534 // the recv operation will not trigger a "CpuAction::on_state_change". This means
535 // that the next trigger would be the 2nd compute, hence ignoring the idle time
536 // during the recv call. By updating at the beginning of a compute, we can
537 // fix that. (If the cpu is not idle, this is not required.)
538 simgrid::s4u::Exec::on_start.connect([](simgrid::s4u::Actor const&, simgrid::s4u::Exec const& activity) {
539 if (activity.get_host_number() == 1) { // We only run on one host
540 simgrid::s4u::Host* host = activity.get_host();
541 simgrid::s4u::VirtualMachine* vm = dynamic_cast<simgrid::s4u::VirtualMachine*>(host);
544 xbt_assert(host != nullptr);
545 host->extension<HostEnergy>()->update();
550 /** @ingroup plugin_host_energy
551 * @brief updates the consumption of all hosts
553 * After this call, sg_host_get_consumed_energy() will not interrupt your process
554 * (until after the next clock update).
556 void sg_host_energy_update_all()
558 simgrid::kernel::actor::simcall([]() {
559 std::vector<simgrid::s4u::Host*> list = simgrid::s4u::Engine::get_instance()->get_all_hosts();
560 for (auto const& host : list)
561 if (dynamic_cast<simgrid::s4u::VirtualMachine*>(host) == nullptr) { // Ignore virtual machines
562 xbt_assert(host != nullptr);
563 host->extension<HostEnergy>()->update();
568 /** @ingroup plugin_host_energy
569 * @brief Returns the total energy consumed by the host so far (in Joules)
571 * Please note that since the consumption is lazily updated, it may require a simcall to update it.
572 * The result is that the actor requesting this value will be interrupted,
573 * the value will be updated in kernel mode before returning the control to the requesting actor.
575 double sg_host_get_consumed_energy(sg_host_t host)
577 xbt_assert(HostEnergy::EXTENSION_ID.valid(),
578 "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
579 return host->extension<HostEnergy>()->get_consumed_energy();
582 /** @ingroup plugin_host_energy
583 * @brief Get the amount of watt dissipated when the host is idling
585 double sg_host_get_idle_consumption(sg_host_t host)
587 xbt_assert(HostEnergy::EXTENSION_ID.valid(),
588 "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
589 return host->extension<HostEnergy>()->get_idle_consumption();
592 /** @ingroup plugin_host_energy
593 * @brief Get the amount of watt dissipated at the given pstate when the host is idling
595 double sg_host_get_wattmin_at(sg_host_t host, int pstate)
597 xbt_assert(HostEnergy::EXTENSION_ID.valid(),
598 "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
599 return host->extension<HostEnergy>()->get_watt_min_at(pstate);
601 /** @ingroup plugin_host_energy
602 * @brief Returns the amount of watt dissipated at the given pstate when the host burns CPU at 100%
604 double sg_host_get_wattmax_at(sg_host_t host, int pstate)
606 xbt_assert(HostEnergy::EXTENSION_ID.valid(),
607 "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
608 return host->extension<HostEnergy>()->get_watt_max_at(pstate);
610 /** @ingroup plugin_host_energy
611 * @brief Returns the power slope at the given pstate
613 double sg_host_get_power_range_slope_at(sg_host_t host, int pstate)
615 xbt_assert(HostEnergy::EXTENSION_ID.valid(),
616 "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
617 return host->extension<HostEnergy>()->get_power_range_slope_at(pstate);
619 /** @ingroup plugin_host_energy
620 * @brief Returns the current consumption of the host
622 double sg_host_get_current_consumption(sg_host_t host)
624 xbt_assert(HostEnergy::EXTENSION_ID.valid(),
625 "The Energy plugin is not active. Please call sg_host_energy_plugin_init() during initialization.");
626 return host->extension<HostEnergy>()->get_current_watts_value();