2012-11-02 17:32:01 +01:00
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/*
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2015-07-07 10:51:04 +02:00
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* Copyright (c) 2012, 2015 ARM Limited
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2012-11-02 17:32:01 +01:00
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* All rights reserved
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*
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* The license below extends only to copyright in the software and shall
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* not be construed as granting a license to any other intellectual
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* property including but not limited to intellectual property relating
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* to a hardware implementation of the functionality of the software
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* licensed hereunder. You may use the software subject to the license
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* terms below provided that you ensure that this notice is replicated
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* unmodified and in its entirety in all distributions of the software,
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* modified or unmodified, in source code or in binary form.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are
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* met: redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer;
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* redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution;
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* neither the name of the copyright holders nor the names of its
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* contributors may be used to endorse or promote products derived from
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* this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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* A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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* OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*
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* Authors: Andreas Sandberg
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*/
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#ifndef __SIM_DRAIN_HH__
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#define __SIM_DRAIN_HH__
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2015-07-07 10:51:05 +02:00
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#include <atomic>
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#include <mutex>
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#include <unordered_set>
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2012-11-02 17:32:01 +01:00
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2015-07-07 10:51:04 +02:00
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class Drainable;
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#ifndef SWIG // SWIG doesn't support strongly typed enums
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/**
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* Object drain/handover states
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*
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* An object starts out in the Running state. When the simulator
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* prepares to take a snapshot or prepares a CPU for handover, it
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* calls the drain() method to transfer the object into the Draining
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* or Drained state. If any object enters the Draining state
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* (Drainable::drain() returning >0), simulation continues until it
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* all objects have entered the Drained state.
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*
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* Before resuming simulation, the simulator calls resume() to
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* transfer the object to the Running state.
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*
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* \note Even though the state of an object (visible to the rest of
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* the world through Drainable::getState()) could be used to determine
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* if all objects have entered the Drained state, the protocol is
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* actually a bit more elaborate. See Drainable::drain() for details.
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*/
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enum class DrainState {
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Running, /** Running normally */
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Draining, /** Draining buffers pending serialization/handover */
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Drained /** Buffers drained, ready for serialization/handover */
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};
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#endif
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2012-11-02 17:32:01 +01:00
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/**
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* This class coordinates draining of a System.
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*
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* When draining the simulator, we need to make sure that all
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* Drainable objects within the system have ended up in the drained
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* state before declaring the operation to be successful. This class
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* keeps track of how many objects are still in the process of
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* draining. Once it determines that all objects have drained their
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* state, it exits the simulation loop.
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2012-11-02 17:32:01 +01:00
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*
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* @note A System might not be completely drained even though the
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* DrainManager has caused the simulation loop to exit. Draining needs
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* to be restarted until all Drainable objects declare that they don't
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* need further simulation to be completely drained. See Drainable for
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* more information.
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*/
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class DrainManager
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{
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private:
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DrainManager();
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#ifndef SWIG
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DrainManager(DrainManager &) = delete;
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#endif
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~DrainManager();
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public:
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/** Get the singleton DrainManager instance */
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static DrainManager &instance() { return _instance; }
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/**
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* Try to drain the system.
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*
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* Try to drain the system and return true if all objects are in a
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* the Drained state at which point the whole simulator is in a
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* consistent state and ready for checkpointing or CPU
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* handover. The simulation script must continue simulating until
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* the simulation loop returns "Finished drain", at which point
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* this method should be called again. This cycle should continue
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* until this method returns true.
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*
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* @return true if all objects were drained successfully, false if
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* more simulation is needed.
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*/
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bool tryDrain();
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/**
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* Resume normal simulation in a Drained system.
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*/
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void resume();
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/**
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* Run state fixups before a checkpoint restore operation
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*
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* The drain state of an object isn't stored in a checkpoint since
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* the whole system is always going to be in the Drained state
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* when the checkpoint is created. When the checkpoint is restored
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* at a later stage, recreated objects will be in the Running
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* state since the state isn't stored in checkpoints. This method
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* performs state fixups on all Drainable objects and the
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* DrainManager itself.
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2012-11-02 17:32:01 +01:00
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*/
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void preCheckpointRestore();
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/** Check if the system is drained */
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bool isDrained() const { return _state == DrainState::Drained; }
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2012-11-02 17:32:01 +01:00
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/** Get the simulators global drain state */
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DrainState state() const { return _state; }
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2012-11-02 17:32:01 +01:00
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/**
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* Notify the DrainManager that a Drainable object has finished
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* draining.
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*/
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void signalDrainDone();
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2012-11-02 17:32:01 +01:00
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public:
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void registerDrainable(Drainable *obj);
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void unregisterDrainable(Drainable *obj);
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private:
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2012-11-02 17:32:01 +01:00
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/**
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* Thread-safe helper function to get the number of Drainable
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* objects in a system.
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2012-11-02 17:32:01 +01:00
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*/
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size_t drainableCount() const;
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2012-11-02 17:32:01 +01:00
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2015-07-07 10:51:05 +02:00
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/** Lock protecting the set of drainable objects */
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mutable std::mutex globalLock;
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/** Set of all drainable objects */
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std::unordered_set<Drainable *> _allDrainable;
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/**
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* Number of objects still draining. This is flagged atomic since
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* it can be manipulated by SimObjects living in different
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* threads.
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*/
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std::atomic_uint _count;
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/** Global simulator drain state */
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DrainState _state;
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/** Singleton instance of the drain manager */
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static DrainManager _instance;
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2012-11-02 17:32:01 +01:00
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};
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/**
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* Interface for objects that might require draining before
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* checkpointing.
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*
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* An object's internal state needs to be drained when creating a
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* checkpoint, switching between CPU models, or switching between
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* timing models. Once the internal state has been drained from
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* <i>all</i> objects in the simulator, the objects are serialized to
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* disc or the configuration change takes place. The process works as
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* follows (see simulate.py for details):
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*
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* <ol>
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* <li>DrainManager::tryDrain() calls Drainable::drain() for every
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* object in the system. Draining has completed if all of them
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* return true. Otherwise, the drain manager keeps track of the
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* objects that requested draining and waits for them to signal
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* that they are done draining using the signalDrainDone() method.
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*
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* <li>Continue simulation. When an object has finished draining its
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* internal state, it calls DrainManager::signalDrainDone() on the
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* manager. The drain manager keeps track of the objects that
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* haven't drained yet, simulation stops when the set of
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* non-drained objects becomes empty.
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*
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* <li>Check if any object still needs draining
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* (DrainManager::tryDrain()), if so repeat the process above.
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*
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* <li>Serialize objects, switch CPU model, or change timing model.
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*
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* <li>Call DrainManager::resume(), which in turn calls
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* Drainable::drainResume() for all objects, and then continue the
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* simulation.
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2012-11-02 17:32:01 +01:00
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* </ol>
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*
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*/
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class Drainable
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{
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friend class DrainManager;
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protected:
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Drainable();
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virtual ~Drainable();
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/**
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* Notify an object that it needs to drain its state.
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*
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* If the object does not need further simulation to drain
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* internal buffers, it returns DrainState::Drained and
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* automatically switches to the Drained state. If the object
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* needs more simulation, it returns DrainState::Draining and
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* automatically enters the Draining state. Other return values
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* are invalid.
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*
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* @note An object that has entered the Drained state can be
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* disturbed by other objects in the system and consequently stop
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* being drained. These perturbations are not visible in the drain
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* state. The simulator therefore repeats the draining process
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* until all objects return DrainState::Drained on the first call
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* to drain().
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*
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* @return DrainState::Drained if the object is drained at this
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* point in time, DrainState::Draining if it needs further
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* simulation.
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2012-11-02 17:32:01 +01:00
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*/
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virtual DrainState drain() = 0;
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/**
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* Resume execution after a successful drain.
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*/
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virtual void drainResume() {};
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/**
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* Signal that an object is drained
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*
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* This method is designed to be called whenever an object enters
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* into a state where it is ready to be drained. The method is
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* safe to call multiple times and there is no need to check that
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* draining has been requested before calling this method.
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*/
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void signalDrainDone() const {
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switch (_drainState) {
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case DrainState::Running:
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case DrainState::Drained:
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return;
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case DrainState::Draining:
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_drainState = DrainState::Drained;
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_drainManager.signalDrainDone();
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return;
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}
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}
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public:
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/** Return the current drain state of an object. */
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DrainState drainState() const { return _drainState; }
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2015-11-26 11:03:43 +01:00
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/**
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* Notify a child process of a fork.
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*
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* When calling fork in gem5, we need to ensure that resources
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* shared between the parent and the child are consistent. This
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* method is intended to be overloaded to handle that. For
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* example, an object could use this method to re-open input files
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* to get a separate file description with a private file offset.
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*
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* This method is only called in the child of the fork. The call
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* takes place in a drained system.
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*/
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virtual void notifyFork() {};
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private:
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/** DrainManager interface to request a drain operation */
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DrainState dmDrain();
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/** DrainManager interface to request a resume operation */
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void dmDrainResume();
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/** Convenience reference to the drain manager */
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DrainManager &_drainManager;
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/**
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* Current drain state of the object. Needs to be mutable since
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* objects need to be able to signal that they have transitioned
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* into a Drained state even if the calling method is const.
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*/
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mutable DrainState _drainState;
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};
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#endif
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