drain.hh revision 10912
1/* 2 * Copyright (c) 2012, 2015 ARM Limited 3 * All rights reserved 4 * 5 * The license below extends only to copyright in the software and shall 6 * not be construed as granting a license to any other intellectual 7 * property including but not limited to intellectual property relating 8 * to a hardware implementation of the functionality of the software 9 * licensed hereunder. You may use the software subject to the license 10 * terms below provided that you ensure that this notice is replicated 11 * unmodified and in its entirety in all distributions of the software, 12 * modified or unmodified, in source code or in binary form. 13 * 14 * Redistribution and use in source and binary forms, with or without 15 * modification, are permitted provided that the following conditions are 16 * met: redistributions of source code must retain the above copyright 17 * notice, this list of conditions and the following disclaimer; 18 * redistributions in binary form must reproduce the above copyright 19 * notice, this list of conditions and the following disclaimer in the 20 * documentation and/or other materials provided with the distribution; 21 * neither the name of the copyright holders nor the names of its 22 * contributors may be used to endorse or promote products derived from 23 * this software without specific prior written permission. 24 * 25 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 26 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 27 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 28 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 29 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 30 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 31 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 32 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 33 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 34 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 35 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 36 * 37 * Authors: Andreas Sandberg 38 */ 39 40#ifndef __SIM_DRAIN_HH__ 41#define __SIM_DRAIN_HH__ 42 43#include <atomic> 44#include <mutex> 45#include <unordered_set> 46 47#include "base/flags.hh" 48 49class Drainable; 50 51#ifndef SWIG // SWIG doesn't support strongly typed enums 52/** 53 * Object drain/handover states 54 * 55 * An object starts out in the Running state. When the simulator 56 * prepares to take a snapshot or prepares a CPU for handover, it 57 * calls the drain() method to transfer the object into the Draining 58 * or Drained state. If any object enters the Draining state 59 * (Drainable::drain() returning >0), simulation continues until it 60 * all objects have entered the Drained state. 61 * 62 * Before resuming simulation, the simulator calls resume() to 63 * transfer the object to the Running state. 64 * 65 * \note Even though the state of an object (visible to the rest of 66 * the world through Drainable::getState()) could be used to determine 67 * if all objects have entered the Drained state, the protocol is 68 * actually a bit more elaborate. See Drainable::drain() for details. 69 */ 70enum class DrainState { 71 Running, /** Running normally */ 72 Draining, /** Draining buffers pending serialization/handover */ 73 Drained /** Buffers drained, ready for serialization/handover */ 74}; 75#endif 76 77/** 78 * This class coordinates draining of a System. 79 * 80 * When draining the simulator, we need to make sure that all 81 * Drainable objects within the system have ended up in the drained 82 * state before declaring the operation to be successful. This class 83 * keeps track of how many objects are still in the process of 84 * draining. Once it determines that all objects have drained their 85 * state, it exits the simulation loop. 86 * 87 * @note A System might not be completely drained even though the 88 * DrainManager has caused the simulation loop to exit. Draining needs 89 * to be restarted until all Drainable objects declare that they don't 90 * need further simulation to be completely drained. See Drainable for 91 * more information. 92 */ 93class DrainManager 94{ 95 private: 96 DrainManager(); 97#ifndef SWIG 98 DrainManager(DrainManager &) = delete; 99#endif 100 ~DrainManager(); 101 102 public: 103 /** Get the singleton DrainManager instance */ 104 static DrainManager &instance() { return _instance; } 105 106 /** 107 * Try to drain the system. 108 * 109 * Try to drain the system and return true if all objects are in a 110 * the Drained state at which point the whole simulator is in a 111 * consistent state and ready for checkpointing or CPU 112 * handover. The simulation script must continue simulating until 113 * the simulation loop returns "Finished drain", at which point 114 * this method should be called again. This cycle should continue 115 * until this method returns true. 116 * 117 * @return true if all objects were drained successfully, false if 118 * more simulation is needed. 119 */ 120 bool tryDrain(); 121 122 /** 123 * Resume normal simulation in a Drained system. 124 */ 125 void resume(); 126 127 /** 128 * Run state fixups before a checkpoint restore operation 129 * 130 * The drain state of an object isn't stored in a checkpoint since 131 * the whole system is always going to be in the Drained state 132 * when the checkpoint is created. When the checkpoint is restored 133 * at a later stage, recreated objects will be in the Running 134 * state since the state isn't stored in checkpoints. This method 135 * performs state fixups on all Drainable objects and the 136 * DrainManager itself. 137 */ 138 void preCheckpointRestore(); 139 140 /** Check if the system is drained */ 141 bool isDrained() { return _state == DrainState::Drained; } 142 143 /** Get the simulators global drain state */ 144 DrainState state() { return _state; } 145 146 /** 147 * Notify the DrainManager that a Drainable object has finished 148 * draining. 149 */ 150 void signalDrainDone(); 151 152 public: 153 void registerDrainable(Drainable *obj); 154 void unregisterDrainable(Drainable *obj); 155 156 private: 157 /** 158 * Thread-safe helper function to get the number of Drainable 159 * objects in a system. 160 */ 161 size_t drainableCount() const; 162 163 /** Lock protecting the set of drainable objects */ 164 mutable std::mutex globalLock; 165 166 /** Set of all drainable objects */ 167 std::unordered_set<Drainable *> _allDrainable; 168 169 /** 170 * Number of objects still draining. This is flagged atomic since 171 * it can be manipulated by SimObjects living in different 172 * threads. 173 */ 174 std::atomic_uint _count; 175 176 /** Global simulator drain state */ 177 DrainState _state; 178 179 /** Singleton instance of the drain manager */ 180 static DrainManager _instance; 181}; 182 183/** 184 * Interface for objects that might require draining before 185 * checkpointing. 186 * 187 * An object's internal state needs to be drained when creating a 188 * checkpoint, switching between CPU models, or switching between 189 * timing models. Once the internal state has been drained from 190 * <i>all</i> objects in the simulator, the objects are serialized to 191 * disc or the configuration change takes place. The process works as 192 * follows (see simulate.py for details): 193 * 194 * <ol> 195 * <li>Call Drainable::drain() for every object in the 196 * system. Draining has completed if all of them return 197 * zero. Otherwise, the sum of the return values is loaded into 198 * the counter of the DrainManager. A pointer to the drain 199 * manager is passed as an argument to the drain() method. 200 * 201 * <li>Continue simulation. When an object has finished draining its 202 * internal state, it calls DrainManager::signalDrainDone() on the 203 * manager. When the counter in the manager reaches zero, the 204 * simulation stops. 205 * 206 * <li>Check if any object still needs draining, if so repeat the 207 * process above. 208 * 209 * <li>Serialize objects, switch CPU model, or change timing model. 210 * 211 * <li>Call Drainable::drainResume() and continue the simulation. 212 * </ol> 213 * 214 */ 215class Drainable 216{ 217 friend class DrainManager; 218 219 public: 220 Drainable(); 221 virtual ~Drainable(); 222 223 /** 224 * Determine if an object needs draining and register a 225 * DrainManager. 226 * 227 * When draining the state of an object, the simulator calls drain 228 * with a pointer to a drain manager. If the object does not need 229 * further simulation to drain internal buffers, it switched to 230 * the Drained state and returns 0, otherwise it switches to the 231 * Draining state and returns the number of times that it will 232 * call Event::process() on the drain event. Most objects are 233 * expected to return either 0 or 1. 234 * 235 * @note An object that has entered the Drained state can be 236 * disturbed by other objects in the system and consequently be 237 * forced to enter the Draining state again. The simulator 238 * therefore repeats the draining process until all objects return 239 * 0 on the first call to drain(). 240 * 241 * @param drainManager DrainManager to use to inform the simulator 242 * when draining has completed. 243 * 244 * @return 0 if the object is ready for serialization now, >0 if 245 * it needs further simulation. 246 */ 247 virtual unsigned int drain(DrainManager *drainManager) = 0; 248 249 /** 250 * Resume execution after a successful drain. 251 * 252 * @note This method is normally only called from the simulation 253 * scripts. 254 */ 255 virtual void drainResume(); 256 257 DrainState getDrainState() const { return _drainState; } 258 259 protected: 260 void setDrainState(DrainState new_state) { _drainState = new_state; } 261 262 private: 263 DrainManager &_drainManager; 264 DrainState _drainState; 265}; 266 267#endif 268