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 *
84 * The readyEvent runs the first two steps of the delta cycle. It first goes
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
94 * the evaluate or update phase above. Because those are scheduled at the
95 * normal priority, they will now happen together until there aren't any
96 * delta events left.
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
99 * readyEvent will have been scheduled and will have been waiting patiently
100 * behind the delta notification events. That will now run, effectively
101 * starting the next delta cycle.
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
106 * events until it comes across a timed notification, aka a notification
107 * scheduled to happen in the future. Like delta notification events, those
108 * will all happen together since the readyEvent priority is lower,
109 * potentially marking new processes as ready. Once these events finish, the
110 * readyEvent may run, starting the next delta cycle.
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
190 schedule(::Event *event, Tick tick)
213 schedule(ScEvent *event, const ::sc_core::sc_time &delay)
214 {
192 pendingTicks[tick]++;
215 Tick tick = delayed(delay);
216 event->schedule(tick);
217
194 if (initReady)
195 eq->schedule(event, tick);
196 else
197 eventsToSchedule[event] = tick;
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
202 deschedule(::Event *event)
239 deschedule(ScEvent *event)
240 {
204 auto it = pendingTicks.find(event->when());
205 if (--it->second == 0)
206 pendingTicks.erase(it);
241 if (event->when() == getCurTick()) {
242 // Remove from delta notifications.
243 deltas.erase(event);
244 event->deschedule();
245 return;
246 }
247
208 if (initReady)
209 eq->deschedule(event);
210 else
211 eventsToSchedule.erase(event);
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
214 // Tell the scheduler than an event fired for bookkeeping purposes.
267 void
216 eventHappened()
268 completeTimeSlot(TimeSlot *ts)
269 {
218 auto it = pendingTicks.begin();
219 if (--it->second == 0)
220 pendingTicks.erase(it);
221
222 if (starved() && !runToTime)
223 scheduleStarvationEvent();
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 {
237 if (!readyList.empty() || !updateList.empty())
238 return true;
239 return pendingTicks.size() &&
240 pendingTicks.begin()->first == getCurTick();
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 {
247 switch (pendingTicks.size()) {
248 case 0: return false;
249 case 1: return pendingTicks.begin()->first > getCurTick();
250 default: return true;
251 }
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 {
258 if (!readyList.empty() || !updateList.empty())
299 if (pendingCurr())
300 return 0;
260 else if (pendingTicks.size())
261 return pendingTicks.begin()->first - getCurTick();
262 else
263 return MaxTick - getCurTick();
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;
291 std::map<Tick, int> pendingTicks;
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 {
306 return (readyList.empty() && updateList.empty() &&
307 (pendingTicks.empty() ||
308 pendingTicks.begin()->first > maxTick) &&
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__