scheduler.hh revision 13063
1/* 2 * Copyright 2018 Google, Inc. 3 * 4 * Redistribution and use in source and binary forms, with or without 5 * modification, are permitted provided that the following conditions are 6 * met: redistributions of source code must retain the above copyright 7 * notice, this list of conditions and the following disclaimer; 8 * redistributions in binary form must reproduce the above copyright 9 * notice, this list of conditions and the following disclaimer in the 10 * documentation and/or other materials provided with the distribution; 11 * neither the name of the copyright holders nor the names of its 12 * contributors may be used to endorse or promote products derived from 13 * this software without specific prior written permission. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 16 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 17 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 18 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 19 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 21 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 25 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 * 27 * Authors: Gabe Black 28 */ 29 30#ifndef __SYSTEMC_CORE_SCHEDULER_HH__ 31#define __SYSTEMC_CORE_SCHEDULER_HH__ 32 33#include <functional> 34#include <map> 35#include <set> 36#include <vector> 37 38#include "base/logging.hh" 39#include "sim/core.hh" 40#include "sim/eventq.hh" 41#include "systemc/core/channel.hh" 42#include "systemc/core/list.hh" 43#include "systemc/core/process.hh" 44#include "systemc/core/sched_event.hh" 45 46class Fiber; 47 48namespace sc_gem5 49{ 50 51typedef NodeList<Process> ProcessList; 52typedef NodeList<Channel> ChannelList; 53 54/* 55 * The scheduler supports three different mechanisms, the initialization phase, 56 * delta cycles, and timed notifications. 57 * 58 * INITIALIZATION PHASE 59 * 60 * The initialization phase has three parts: 61 * 1. Run requested channel updates. 62 * 2. Make processes which need to initialize runnable (methods and threads 63 * which didn't have dont_initialize called on them). 64 * 3. Process delta notifications. 65 * 66 * First, the Kernel SimObject calls the update() method during its startup() 67 * callback which handles the requested channel updates. The Kernel also 68 * schedules an event to be run at time 0 with a slightly elevated priority 69 * so that it happens before any "normal" event. 70 * 71 * When that t0 event happens, it calls the schedulers prepareForInit method 72 * which performs step 2 above. That indirectly causes the scheduler's 73 * readyEvent to be scheduled with slightly lowered priority, ensuring it 74 * happens after any "normal" event. 75 * 76 * Because delta notifications are scheduled at the standard priority, all 77 * of those events will happen next, performing step 3 above. Once they finish, 78 * if the readyEvent was scheduled above, there shouldn't be any higher 79 * priority events in front of it. When it runs, it will start the first 80 * evaluate phase of the first delta cycle. 81 * 82 * DELTA CYCLE 83 * 84 * A delta cycle has three phases within it. 85 * 1. The evaluate phase where runnable processes are allowed to run. 86 * 2. The update phase where requested channel updates hapen. 87 * 3. The delta notification phase where delta notifications happen. 88 * 89 * The readyEvent runs all three steps of the delta cycle. It first goes 90 * through the list of runnable processes and executes them until the set is 91 * empty, and then immediately runs the update phase. Since these are all part 92 * of the same event, there's no chance for other events to intervene and 93 * break the required order above. 94 * 95 * During the update phase above, the spec forbids any action which would make 96 * a process runnable. That means that once the update phase finishes, the set 97 * of runnable processes will be empty. There may, however, have been some 98 * delta notifications/timeouts which will have been scheduled during either 99 * the evaluate or update phase above. Those will have been accumulated in the 100 * scheduler, and are now all executed. 101 * 102 * If any processes became runnable during the delta notification phase, the 103 * readyEvent will have been scheduled and will be waiting and ready to run 104 * again, effectively starting the next delta cycle. 105 * 106 * TIMED NOTIFICATION PHASE 107 * 108 * If no processes became runnable, the event queue will continue to process 109 * events until it comes across an event which represents all the timed 110 * notifications which are supposed to happen at a particular time. The object 111 * which tracks them will execute all those notifications, and then destroy 112 * itself. If the readyEvent is now ready to run, the next delta cycle will 113 * start. 114 * 115 * PAUSE/STOP 116 * 117 * To inject a pause from sc_pause which should happen after the current delta 118 * cycle's delta notification phase, an event is scheduled with a lower than 119 * normal priority, but higher than the readyEvent. That ensures that any 120 * delta notifications which are scheduled with normal priority will happen 121 * first, since those are part of the current delta cycle. Then the pause 122 * event will happen before the next readyEvent which would start the next 123 * delta cycle. All of these events are scheduled for the current time, and so 124 * would happen before any timed notifications went off. 125 * 126 * To inject a stop from sc_stop, the delta cycles should stop before even the 127 * delta notifications have happened, but after the evaluate and update phases. 128 * For that, a stop event with slightly higher than normal priority will be 129 * scheduled so that it happens before any of the delta notification events 130 * which are at normal priority. 131 * 132 * MAX RUN TIME 133 * 134 * When sc_start is called, it's possible to pass in a maximum time the 135 * simulation should run to, at which point sc_pause is implicitly called. The 136 * simulation is supposed to run up to the latest timed notification phase 137 * which is less than or equal to the maximum time. In other words it should 138 * run timed notifications at the maximum time, but not the subsequent evaluate 139 * phase. That's implemented by scheduling an event at the max time with a 140 * priority which is lower than all the others except the ready event. Timed 141 * notifications will happen before it fires, but it will override any ready 142 * event and prevent the evaluate phase from starting. 143 */ 144 145class Scheduler 146{ 147 public: 148 typedef std::set<ScEvent *> ScEvents; 149 150 class TimeSlot : public ::Event 151 { 152 public: 153 TimeSlot() : ::Event(Default_Pri, AutoDelete) {} 154 155 ScEvents events; 156 void process(); 157 }; 158 159 typedef std::map<Tick, TimeSlot *> TimeSlots; 160 161 Scheduler(); 162 163 const std::string name() const { return "systemc_scheduler"; } 164 165 uint64_t numCycles() { return _numCycles; } 166 Process *current() { return _current; } 167 168 // Prepare for initialization. 169 void prepareForInit(); 170 171 // Register a process with the scheduler. 172 void reg(Process *p); 173 174 // Tell the scheduler not to initialize a process. 175 void dontInitialize(Process *p); 176 177 // Run the next process, if there is one. 178 void yield(); 179 180 // Put a process on the ready list. 181 void ready(Process *p); 182 183 // Schedule an update for a given channel. 184 void requestUpdate(Channel *c); 185 186 // Run the given process immediately, preempting whatever may be running. 187 void 188 runNow(Process *p) 189 { 190 // If a process is running, schedule it/us to run again. 191 if (_current) 192 readyList.pushFirst(_current); 193 // Schedule p to run first. 194 readyList.pushFirst(p); 195 yield(); 196 } 197 198 // Set an event queue for scheduling events. 199 void setEventQueue(EventQueue *_eq) { eq = _eq; } 200 201 // Get the current time according to gem5. 202 Tick getCurTick() { return eq ? eq->getCurTick() : 0; } 203 204 Tick 205 delayed(const ::sc_core::sc_time &delay) 206 { 207 //XXX We're assuming the systemc time resolution is in ps. 208 return getCurTick() + delay.value() * SimClock::Int::ps; 209 } 210 211 // For scheduling delayed/timed notifications/timeouts. 212 void 213 schedule(ScEvent *event, const ::sc_core::sc_time &delay) 214 { 215 Tick tick = delayed(delay); 216 event->schedule(tick); 217 218 // Delta notification/timeout. 219 if (delay.value() == 0) { 220 deltas.insert(event); 221 scheduleReadyEvent(); 222 return; 223 } 224 225 // Timed notification/timeout. 226 TimeSlot *&ts = timeSlots[tick]; 227 if (!ts) { 228 ts = new TimeSlot; 229 if (initReady) 230 eq->schedule(ts, tick); 231 else 232 eventsToSchedule[ts] = tick; 233 } 234 ts->events.insert(event); 235 } 236 237 // For descheduling delayed/timed notifications/timeouts. 238 void 239 deschedule(ScEvent *event) 240 { 241 if (event->when() == getCurTick()) { 242 // Remove from delta notifications. 243 deltas.erase(event); 244 event->deschedule(); 245 return; 246 } 247 248 // Timed notification/timeout. 249 auto tsit = timeSlots.find(event->when()); 250 panic_if(tsit == timeSlots.end(), 251 "Descheduling event at time with no events."); 252 TimeSlot *ts = tsit->second; 253 ScEvents &events = ts->events; 254 events.erase(event); 255 event->deschedule(); 256 257 // If no more events are happening at this time slot, get rid of it. 258 if (events.empty()) { 259 if (initReady) 260 eq->deschedule(ts); 261 else 262 eventsToSchedule.erase(ts); 263 timeSlots.erase(tsit); 264 } 265 } 266 267 void 268 completeTimeSlot(TimeSlot *ts) 269 { 270 assert(ts == timeSlots.begin()->second); 271 timeSlots.erase(timeSlots.begin()); 272 } 273 274 // Pending activity ignores gem5 activity, much like how a systemc 275 // simulation wouldn't know about asynchronous external events (socket IO 276 // for instance) that might happen before time advances in a pure 277 // systemc simulation. Also the spec lists what specific types of pending 278 // activity needs to be counted, which obviously doesn't include gem5 279 // events. 280 281 // Return whether there's pending systemc activity at this time. 282 bool 283 pendingCurr() 284 { 285 return !readyList.empty() || !updateList.empty() || !deltas.empty(); 286 } 287 288 // Return whether there are pending timed notifications or timeouts. 289 bool 290 pendingFuture() 291 { 292 return !timeSlots.empty(); 293 } 294 295 // Return how many ticks there are until the first pending event, if any. 296 Tick 297 timeToPending() 298 { 299 if (pendingCurr()) 300 return 0; 301 if (pendingFuture()) 302 return timeSlots.begin()->first - getCurTick(); 303 return MaxTick - getCurTick(); 304 } 305 306 // Run scheduled channel updates. 307 void update(); 308 309 void setScMainFiber(Fiber *sc_main) { scMain = sc_main; } 310 311 void start(Tick max_tick, bool run_to_time); 312 void oneCycle(); 313 314 void schedulePause(); 315 void scheduleStop(bool finish_delta); 316 317 bool paused() { return _paused; } 318 bool stopped() { return _stopped; } 319 320 private: 321 typedef const EventBase::Priority Priority; 322 static Priority DefaultPriority = EventBase::Default_Pri; 323 324 static Priority StopPriority = DefaultPriority - 1; 325 static Priority PausePriority = DefaultPriority + 1; 326 static Priority MaxTickPriority = DefaultPriority + 2; 327 static Priority ReadyPriority = DefaultPriority + 3; 328 static Priority StarvationPriority = ReadyPriority; 329 330 EventQueue *eq; 331 332 ScEvents deltas; 333 TimeSlots timeSlots; 334 335 void runReady(); 336 EventWrapper<Scheduler, &Scheduler::runReady> readyEvent; 337 void scheduleReadyEvent(); 338 339 void pause(); 340 void stop(); 341 EventWrapper<Scheduler, &Scheduler::pause> pauseEvent; 342 EventWrapper<Scheduler, &Scheduler::stop> stopEvent; 343 Fiber *scMain; 344 345 bool 346 starved() 347 { 348 return (readyList.empty() && updateList.empty() && deltas.empty() && 349 (timeSlots.empty() || timeSlots.begin()->first > maxTick) && 350 initList.empty()); 351 } 352 EventWrapper<Scheduler, &Scheduler::pause> starvationEvent; 353 void scheduleStarvationEvent(); 354 355 bool _started; 356 bool _paused; 357 bool _stopped; 358 359 Tick maxTick; 360 EventWrapper<Scheduler, &Scheduler::pause> maxTickEvent; 361 362 uint64_t _numCycles; 363 364 Process *_current; 365 366 bool initReady; 367 bool runToTime; 368 bool runOnce; 369 370 ProcessList initList; 371 ProcessList toFinalize; 372 ProcessList readyList; 373 374 ChannelList updateList; 375 376 std::map<::Event *, Tick> eventsToSchedule; 377}; 378 379extern Scheduler scheduler; 380 381inline void 382Scheduler::TimeSlot::process() 383{ 384 for (auto &e: events) 385 e->run(); 386 scheduler.completeTimeSlot(this); 387} 388 389} // namespace sc_gem5 390 391#endif // __SYSTEMC_CORE_SCHEDULER_H__ 392