scheduler.hh revision 13072
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    ~Scheduler();
163
164    const std::string name() const { return "systemc_scheduler"; }
165
166    uint64_t numCycles() { return _numCycles; }
167    Process *current() { return _current; }
168
169    void initPhase();
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            schedule(ts, tick);
230        }
231        ts->events.insert(event);
232    }
233
234    // For descheduling delayed/timed notifications/timeouts.
235    void
236    deschedule(ScEvent *event)
237    {
238        if (event->when() == getCurTick()) {
239            // Remove from delta notifications.
240            deltas.erase(event);
241            event->deschedule();
242            return;
243        }
244
245        // Timed notification/timeout.
246        auto tsit = timeSlots.find(event->when());
247        panic_if(tsit == timeSlots.end(),
248                "Descheduling event at time with no events.");
249        TimeSlot *ts = tsit->second;
250        ScEvents &events = ts->events;
251        events.erase(event);
252        event->deschedule();
253
254        // If no more events are happening at this time slot, get rid of it.
255        if (events.empty()) {
256            deschedule(ts);
257            timeSlots.erase(tsit);
258        }
259    }
260
261    void
262    completeTimeSlot(TimeSlot *ts)
263    {
264        assert(ts == timeSlots.begin()->second);
265        timeSlots.erase(timeSlots.begin());
266    }
267
268    // Pending activity ignores gem5 activity, much like how a systemc
269    // simulation wouldn't know about asynchronous external events (socket IO
270    // for instance) that might happen before time advances in a pure
271    // systemc simulation. Also the spec lists what specific types of pending
272    // activity needs to be counted, which obviously doesn't include gem5
273    // events.
274
275    // Return whether there's pending systemc activity at this time.
276    bool
277    pendingCurr()
278    {
279        return !readyList.empty() || !updateList.empty() || !deltas.empty();
280    }
281
282    // Return whether there are pending timed notifications or timeouts.
283    bool
284    pendingFuture()
285    {
286        return !timeSlots.empty();
287    }
288
289    // Return how many ticks there are until the first pending event, if any.
290    Tick
291    timeToPending()
292    {
293        if (pendingCurr())
294            return 0;
295        if (pendingFuture())
296            return timeSlots.begin()->first - getCurTick();
297        return MaxTick - getCurTick();
298    }
299
300    // Run scheduled channel updates.
301    void update();
302
303    void setScMainFiber(Fiber *sc_main) { scMain = sc_main; }
304
305    void start(Tick max_tick, bool run_to_time);
306    void oneCycle();
307
308    void schedulePause();
309    void scheduleStop(bool finish_delta);
310
311    bool paused() { return _paused; }
312    bool stopped() { return _stopped; }
313
314  private:
315    typedef const EventBase::Priority Priority;
316    static Priority DefaultPriority = EventBase::Default_Pri;
317
318    static Priority StopPriority = DefaultPriority - 1;
319    static Priority PausePriority = DefaultPriority + 1;
320    static Priority MaxTickPriority = DefaultPriority + 2;
321    static Priority ReadyPriority = DefaultPriority + 3;
322    static Priority StarvationPriority = ReadyPriority;
323
324    EventQueue *eq;
325
326    // For gem5 style events.
327    void
328    schedule(::Event *event, Tick tick)
329    {
330        if (initDone)
331            eq->schedule(event, tick);
332        else
333            eventsToSchedule[event] = tick;
334    }
335
336    void schedule(::Event *event) { schedule(event, getCurTick()); }
337
338    void
339    deschedule(::Event *event)
340    {
341        if (initDone)
342            eq->deschedule(event);
343        else
344            eventsToSchedule.erase(event);
345    }
346
347    ScEvents deltas;
348    TimeSlots timeSlots;
349
350    void runReady();
351    EventWrapper<Scheduler, &Scheduler::runReady> readyEvent;
352    void scheduleReadyEvent();
353
354    void pause();
355    void stop();
356    EventWrapper<Scheduler, &Scheduler::pause> pauseEvent;
357    EventWrapper<Scheduler, &Scheduler::stop> stopEvent;
358    Fiber *scMain;
359
360    bool
361    starved()
362    {
363        return (readyList.empty() && updateList.empty() && deltas.empty() &&
364                (timeSlots.empty() || timeSlots.begin()->first > maxTick) &&
365                initList.empty());
366    }
367    EventWrapper<Scheduler, &Scheduler::pause> starvationEvent;
368    void scheduleStarvationEvent();
369
370    bool _started;
371    bool _paused;
372    bool _stopped;
373
374    Tick maxTick;
375    EventWrapper<Scheduler, &Scheduler::pause> maxTickEvent;
376
377    uint64_t _numCycles;
378
379    Process *_current;
380
381    bool initDone;
382    bool runToTime;
383    bool runOnce;
384
385    ProcessList initList;
386    ProcessList toFinalize;
387    ProcessList readyList;
388
389    ChannelList updateList;
390
391    std::map<::Event *, Tick> eventsToSchedule;
392};
393
394extern Scheduler scheduler;
395
396inline void
397Scheduler::TimeSlot::process()
398{
399    for (auto &e: events)
400        e->run();
401    scheduler.completeTimeSlot(this);
402}
403
404} // namespace sc_gem5
405
406#endif // __SYSTEMC_CORE_SCHEDULER_H__
407