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diff --git a/src/doc/power_thermal_model.doxygen b/src/doc/power_thermal_model.doxygen new file mode 100644 index 000000000..8b636ab23 --- /dev/null +++ b/src/doc/power_thermal_model.doxygen @@ -0,0 +1,128 @@ +# Copyright (c) 2016 ARM Limited +# All rights reserved +# +# The license below extends only to copyright in the software and shall +# not be construed as granting a license to any other intellectual +# property including but not limited to intellectual property relating +# to a hardware implementation of the functionality of the software +# licensed hereunder. You may use the software subject to the license +# terms below provided that you ensure that this notice is replicated +# unmodified and in its entirety in all distributions of the software, +# modified or unmodified, in source code or in binary form. +# +# Redistribution and use in source and binary forms, with or without +# modification, are permitted provided that the following conditions are +# met: redistributions of source code must retain the above copyright +# notice, this list of conditions and the following disclaimer; +# redistributions in binary form must reproduce the above copyright +# notice, this list of conditions and the following disclaimer in the +# documentation and/or other materials provided with the distribution; +# neither the name of the copyright holders nor the names of its +# contributors may be used to endorse or promote products derived from +# this software without specific prior written permission. +# +# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR +# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT +# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, +# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY +# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT +# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE +# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +# +# Author: David Guillen Fandos + +/*! \page gem5PowerModel Gem5 Power & Thermal model + + \tableofcontents + + This document gives an overview of the power and thermal modelling + infrastructure in Gem5. The purpose is to give a high level view of + all the pieces involved and how they interact with each other and + the simulator. + + \section gem5_PM_CD Class overview + + Classes involved in the power model are: + + - PowerModel: Represents a power model for a hardware component. + + - PowerModelState: Represents a power model for a hardware component + in a certain power state. It is an abstract class that defines an + interface that must be implemented for each model. + + - MathExprPowerModel: Simple implementation of PowerModelState that + assumes that power can be modeled using a simple power + + Classes involved in the thermal model are: + + - ThermalModel: Contains the system thermal model logic and state. + It performs the power query and temperature update. It also enables + gem5 to query for temperature (for OS reporting). + + - ThermalDomain: Represents an entity that generates heat. It's + essentially a group of SimObjects grouped under a SubSystem component + that have its own thermal behaviour. + + - ThermalNode: Represents a node in the thermal circuital equivalent. + The node has a temperature and interacts with other nodes through + connections (thermal resistors and capacitors). + + - ThermalReference: Temperature reference for the thermal model + (essentially a thermal node with a fixed temperature), can be used + to model air or any other constant temperature domains. + + - ThermalEntity: A thermal component that connects two thermal nodes + and models a thermal impedance between them. This class is just an + abstract interface. + + - ThermalResistor: Implements ThermalEntity to model a thermal resistance + between the two nodes it connects. Thermal resistances model the + capacity of a material to transfer heat (units in K/W). + + - ThermalCapacitor. Implements ThermalEntity to model a thermal + capacitance. Thermal capacitors are used to model material's thermal + capacitance, this is, the ability to change a certain material + temperature (units in J/K). + + \section gem5_thermal Thermal model + + The thermal model works by creating a circuital equivalent of the + simulated platform. Each node in the circuit has a temperature (as + voltage equivalent) and power flows between nodes (as current in a + circuit). + + To build this equivalent temperature model the platform is required + to group the power actors (any component that has a power model) + under SubSystems and attach ThermalDomains to those subsystems. + Other components might also be created (like ThermalReferences) and + connected all together by creating thermal entities (capacitors and + resistors). + + Last step to conclude the thermal model is to create the ThermalModel + instance itself and attach all the instances used to it, so it can + properly update them at runtime. Only one thermal model instance is + supported right now and it will automatically report temperature when + appropriate (ie. platform sensor devices). + + \section gem5_power Power model + + Every ClockedObject has a power model associated. If this power model is + non-null power will be calculated at every stats dump (although it might + be possible to force power evaluation at any other point, if the power + model uses the stats, it is a good idea to keep both events in sync). + The definition of a power model is quite vague in the sense that it is + as flexible as users want it to be. The only enforced contraints so far + is the fact that a power model has several power state models, one for + each possible power state for that hardware block. When it comes to compute + power consumption the power is just the weighted average of each power model. + + A power state model is essentially an interface that allows us to define two + power functions for dynamic and static. As an example implementation a class + called MathExprPowerModel has been provided. This implementation allows the + user to define a power model as an equation involving several statistics. + There's also some automatic (or "magic") variables such as "temp", which + reports temperature. |