scheduler.hh revision 13140
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    void clear();
165
166    const std::string name() const { return "systemc_scheduler"; }
167
168    uint64_t numCycles() { return _numCycles; }
169    Process *current() { return _current; }
170
171    void initPhase();
172
173    // Register a process with the scheduler.
174    void reg(Process *p);
175
176    // Tell the scheduler not to initialize a process.
177    void dontInitialize(Process *p);
178
179    // Run the next process, if there is one.
180    void yield();
181
182    // Put a process on the ready list.
183    void ready(Process *p);
184
185    // Mark a process as ready if init is finished, or put it on the list of
186    // processes to be initialized.
187    void resume(Process *p);
188
189    // Remove a process from the ready/init list if it was on one of them, and
190    // return if it was.
191    bool suspend(Process *p);
192
193    // Schedule an update for a given channel.
194    void requestUpdate(Channel *c);
195
196    // Run the given process immediately, preempting whatever may be running.
197    void
198    runNow(Process *p)
199    {
200        // If a process is running, schedule it/us to run again.
201        if (_current)
202            readyList.pushFirst(_current);
203        // Schedule p to run first.
204        readyList.pushFirst(p);
205        yield();
206    }
207
208    // Set an event queue for scheduling events.
209    void setEventQueue(EventQueue *_eq) { eq = _eq; }
210
211    // Get the current time according to gem5.
212    Tick getCurTick() { return eq ? eq->getCurTick() : 0; }
213
214    Tick
215    delayed(const ::sc_core::sc_time &delay)
216    {
217        //XXX We're assuming the systemc time resolution is in ps.
218        return getCurTick() + delay.value() * SimClock::Int::ps;
219    }
220
221    // For scheduling delayed/timed notifications/timeouts.
222    void
223    schedule(ScEvent *event, const ::sc_core::sc_time &delay)
224    {
225        Tick tick = delayed(delay);
226        if (tick < getCurTick())
227            tick = getCurTick();
228
229        event->schedule(tick);
230
231        // Delta notification/timeout.
232        if (delay.value() == 0) {
233            deltas.insert(event);
234            scheduleReadyEvent();
235            return;
236        }
237
238        // Timed notification/timeout.
239        TimeSlot *&ts = timeSlots[tick];
240        if (!ts) {
241            ts = new TimeSlot;
242            schedule(ts, tick);
243        }
244        ts->events.insert(event);
245    }
246
247    // For descheduling delayed/timed notifications/timeouts.
248    void
249    deschedule(ScEvent *event)
250    {
251        if (event->when() == getCurTick()) {
252            // Attempt to remove from delta notifications.
253            if (deltas.erase(event) == 1) {
254                event->deschedule();
255                return;
256            }
257        }
258
259        // Timed notification/timeout.
260        auto tsit = timeSlots.find(event->when());
261        panic_if(tsit == timeSlots.end(),
262                "Descheduling event at time with no events.");
263        TimeSlot *ts = tsit->second;
264        ScEvents &events = ts->events;
265        assert(events.erase(event));
266        event->deschedule();
267
268        // If no more events are happening at this time slot, get rid of it.
269        if (events.empty()) {
270            deschedule(ts);
271            timeSlots.erase(tsit);
272        }
273    }
274
275    void
276    completeTimeSlot(TimeSlot *ts)
277    {
278        _changeStamp++;
279        assert(ts == timeSlots.begin()->second);
280        timeSlots.erase(timeSlots.begin());
281        if (!runToTime && starved())
282            scheduleStarvationEvent();
283    }
284
285    // Pending activity ignores gem5 activity, much like how a systemc
286    // simulation wouldn't know about asynchronous external events (socket IO
287    // for instance) that might happen before time advances in a pure
288    // systemc simulation. Also the spec lists what specific types of pending
289    // activity needs to be counted, which obviously doesn't include gem5
290    // events.
291
292    // Return whether there's pending systemc activity at this time.
293    bool
294    pendingCurr()
295    {
296        return !readyList.empty() || !updateList.empty() || !deltas.empty();
297    }
298
299    // Return whether there are pending timed notifications or timeouts.
300    bool
301    pendingFuture()
302    {
303        return !timeSlots.empty();
304    }
305
306    // Return how many ticks there are until the first pending event, if any.
307    Tick
308    timeToPending()
309    {
310        if (pendingCurr())
311            return 0;
312        if (pendingFuture())
313            return timeSlots.begin()->first - getCurTick();
314        return MaxTick - getCurTick();
315    }
316
317    // Run scheduled channel updates.
318    void update();
319
320    void setScMainFiber(Fiber *sc_main) { scMain = sc_main; }
321
322    void start(Tick max_tick, bool run_to_time);
323    void oneCycle();
324
325    void schedulePause();
326    void scheduleStop(bool finish_delta);
327
328    bool paused() { return _paused; }
329    bool stopped() { return _stopped; }
330
331    uint64_t changeStamp() { return _changeStamp; }
332
333  private:
334    typedef const EventBase::Priority Priority;
335    static Priority DefaultPriority = EventBase::Default_Pri;
336
337    static Priority StopPriority = DefaultPriority - 1;
338    static Priority PausePriority = DefaultPriority + 1;
339    static Priority MaxTickPriority = DefaultPriority + 2;
340    static Priority ReadyPriority = DefaultPriority + 3;
341    static Priority StarvationPriority = ReadyPriority;
342
343    EventQueue *eq;
344
345    // For gem5 style events.
346    void
347    schedule(::Event *event, Tick tick)
348    {
349        if (initDone)
350            eq->schedule(event, tick);
351        else
352            eventsToSchedule[event] = tick;
353    }
354
355    void schedule(::Event *event) { schedule(event, getCurTick()); }
356
357    void
358    deschedule(::Event *event)
359    {
360        if (initDone)
361            eq->deschedule(event);
362        else
363            eventsToSchedule.erase(event);
364    }
365
366    ScEvents deltas;
367    TimeSlots timeSlots;
368
369    void runReady();
370    EventWrapper<Scheduler, &Scheduler::runReady> readyEvent;
371    void scheduleReadyEvent();
372
373    void pause();
374    void stop();
375    EventWrapper<Scheduler, &Scheduler::pause> pauseEvent;
376    EventWrapper<Scheduler, &Scheduler::stop> stopEvent;
377    Fiber *scMain;
378
379    bool
380    starved()
381    {
382        return (readyList.empty() && updateList.empty() && deltas.empty() &&
383                (timeSlots.empty() || timeSlots.begin()->first > maxTick) &&
384                initList.empty());
385    }
386    EventWrapper<Scheduler, &Scheduler::pause> starvationEvent;
387    void scheduleStarvationEvent();
388
389    bool _started;
390    bool _paused;
391    bool _stopped;
392
393    Tick maxTick;
394    Tick lastReadyTick;
395    void
396    maxTickFunc()
397    {
398        if (lastReadyTick != getCurTick())
399            _changeStamp++;
400        pause();
401    }
402    EventWrapper<Scheduler, &Scheduler::maxTickFunc> maxTickEvent;
403
404    uint64_t _numCycles;
405    uint64_t _changeStamp;
406
407    Process *_current;
408
409    bool initDone;
410    bool runToTime;
411    bool runOnce;
412
413    ProcessList initList;
414    ProcessList toFinalize;
415    ProcessList readyList;
416
417    ChannelList updateList;
418
419    std::map<::Event *, Tick> eventsToSchedule;
420};
421
422extern Scheduler scheduler;
423
424inline void
425Scheduler::TimeSlot::process()
426{
427    for (auto &e: events)
428        e->run();
429    scheduler.completeTimeSlot(this);
430}
431
432} // namespace sc_gem5
433
434#endif // __SYSTEMC_CORE_SCHEDULER_H__
435