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
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259 eq->deschedule(ts); 260 else 261 eventsToSchedule.erase(ts); 262 timeSlots.erase(tsit); 263 } 264 } 265 266 void 267 completeTimeSlot(TimeSlot *ts) 268 { 269 assert(ts == timeSlots.begin()->second); 270 timeSlots.erase(timeSlots.begin()); 271 } 272 273 // Pending activity ignores gem5 activity, much like how a systemc 274 // simulation wouldn't know about asynchronous external events (socket IO 275 // for instance) that might happen before time advances in a pure 276 // systemc simulation. Also the spec lists what specific types of pending 277 // activity needs to be counted, which obviously doesn't include gem5 278 // events. 279 280 // Return whether there's pending systemc activity at this time. 281 bool 282 pendingCurr() 283 { 284 return !readyList.empty() || !updateList.empty() || !deltas.empty(); 285 } 286 287 // Return whether there are pending timed notifications or timeouts. 288 bool 289 pendingFuture() 290 { 291 return !timeSlots.empty(); 292 } 293 294 // Return how many ticks there are until the first pending event, if any. 295 Tick 296 timeToPending() 297 { 298 if (pendingCurr()) 299 return 0; 300 if (pendingFuture()) 301 return timeSlots.begin()->first - getCurTick(); 302 return MaxTick - getCurTick(); 303 } 304 305 // Run scheduled channel updates. 306 void update(); 307 308 void setScMainFiber(Fiber *sc_main) { scMain = sc_main; } 309 310 void start(Tick max_tick, bool run_to_time); 311 void oneCycle(); 312 313 void schedulePause(); 314 void scheduleStop(bool finish_delta); 315 316 bool paused() { return _paused; } 317 bool stopped() { return _stopped; } 318 319 private: 320 typedef const EventBase::Priority Priority; 321 static Priority DefaultPriority = EventBase::Default_Pri; 322 323 static Priority StopPriority = DefaultPriority - 1; 324 static Priority PausePriority = DefaultPriority + 1; 325 static Priority MaxTickPriority = DefaultPriority + 2; 326 static Priority ReadyPriority = DefaultPriority + 3; 327 static Priority StarvationPriority = ReadyPriority; 328 329 EventQueue *eq; 330 331 ScEvents deltas; 332 TimeSlots timeSlots; 333 334 void runReady(); 335 EventWrapper<Scheduler, &Scheduler::runReady> readyEvent; 336 void scheduleReadyEvent(); 337 338 void pause(); 339 void stop(); 340 EventWrapper<Scheduler, &Scheduler::pause> pauseEvent; 341 EventWrapper<Scheduler, &Scheduler::stop> stopEvent; 342 Fiber *scMain; 343 344 bool 345 starved() 346 { 347 return (readyList.empty() && updateList.empty() && deltas.empty() && 348 (timeSlots.empty() || timeSlots.begin()->first > maxTick) && 349 initList.empty()); 350 } 351 EventWrapper<Scheduler, &Scheduler::pause> starvationEvent; 352 void scheduleStarvationEvent(); 353 354 bool _started; 355 bool _paused; 356 bool _stopped; 357 358 Tick maxTick; 359 EventWrapper<Scheduler, &Scheduler::pause> maxTickEvent; 360 361 uint64_t _numCycles; 362 363 Process *_current; 364
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