scheduler.hh revision 12957:e54f9890363d
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 <vector> 34 35#include "sim/eventq.hh" 36#include "systemc/core/channel.hh" 37#include "systemc/core/list.hh" 38#include "systemc/core/process.hh" 39 40namespace sc_gem5 41{ 42 43typedef NodeList<Process> ProcessList; 44typedef NodeList<Channel> ChannelList; 45 46/* 47 * The scheduler supports three different mechanisms, the initialization phase, 48 * delta cycles, and timed notifications. 49 * 50 * INITIALIZATION PHASE 51 * 52 * The initialization phase has three parts: 53 * 1. Run requested channel updates. 54 * 2. Make processes which need to initialize runnable (methods and threads 55 * which didn't have dont_initialize called on them). 56 * 3. Process delta notifications. 57 * 58 * First, the Kernel SimObject calls the update() method during its startup() 59 * callback which handles the requested channel updates. The Kernel also 60 * schedules an event to be run at time 0 with a slightly elevated priority 61 * so that it happens before any "normal" event. 62 * 63 * When that t0 event happens, it calls the schedulers prepareForInit method 64 * which performs step 2 above. That indirectly causes the scheduler's 65 * readyEvent to be scheduled with slightly lowered priority, ensuring it 66 * happens after any "normal" event. 67 * 68 * Because delta notifications are scheduled at the standard priority, all 69 * of those events will happen next, performing step 3 above. Once they finish, 70 * if the readyEvent was scheduled above, there shouldn't be any higher 71 * priority events in front of it. When it runs, it will start the first 72 * evaluate phase of the first delta cycle. 73 * 74 * DELTA CYCLE 75 * 76 * A delta cycle has three phases within it. 77 * 1. The evaluate phase where runnable processes are allowed to run. 78 * 2. The update phase where requested channel updates hapen. 79 * 3. The delta notification phase where delta notifications happen. 80 * 81 * The readyEvent runs the first two steps of the delta cycle. It first goes 82 * through the list of runnable processes and executes them until the set is 83 * empty, and then immediately runs the update phase. Since these are all part 84 * of the same event, there's no chance for other events to intervene and 85 * break the required order above. 86 * 87 * During the update phase above, the spec forbids any action which would make 88 * a process runnable. That means that once the update phase finishes, the set 89 * of runnable processes will be empty. There may, however, have been some 90 * delta notifications/timeouts which will have been scheduled during either 91 * the evaluate or update phase above. Because those are scheduled at the 92 * normal priority, they will now happen together until there aren't any 93 * delta events left. 94 * 95 * If any processes became runnable during the delta notification phase, the 96 * readyEvent will have been scheduled and will have been waiting patiently 97 * behind the delta notification events. That will now run, effectively 98 * starting the next delta cycle. 99 * 100 * TIMED NOTIFICATION PHASE 101 * 102 * If no processes became runnable, the event queue will continue to process 103 * events until it comes across a timed notification, aka a notification 104 * scheduled to happen in the future. Like delta notification events, those 105 * will all happen together since the readyEvent priority is lower, 106 * potentially marking new processes as ready. Once these events finish, the 107 * readyEvent may run, starting the next delta cycle. 108 */ 109 110class Scheduler 111{ 112 public: 113 Scheduler(); 114 115 const std::string name() const { return "systemc_scheduler"; } 116 117 uint64_t numCycles() { return _numCycles; } 118 Process *current() { return _current; } 119 120 // Prepare for initialization. 121 void prepareForInit(); 122 123 // Register a process with the scheduler. 124 void reg(Process *p); 125 126 // Tell the scheduler not to initialize a process. 127 void dontInitialize(Process *p); 128 129 // Run the next process, if there is one. 130 void yield(); 131 132 // Put a process on the ready list. 133 void ready(Process *p); 134 135 // Schedule an update for a given channel. 136 void requestUpdate(Channel *c); 137 138 // Run the given process immediately, preempting whatever may be running. 139 void 140 runNow(Process *p) 141 { 142 // If a process is running, schedule it/us to run again. 143 if (_current) 144 readyList.pushFirst(_current); 145 // Schedule p to run first. 146 readyList.pushFirst(p); 147 yield(); 148 } 149 150 // Set an event queue for scheduling events. 151 void setEventQueue(EventQueue *_eq) { eq = _eq; } 152 153 // Retrieve the event queue. 154 EventQueue &eventQueue() const { return *eq; } 155 156 // Run scheduled channel updates. 157 void update(); 158 159 private: 160 EventQueue *eq; 161 162 void runReady(); 163 EventWrapper<Scheduler, &Scheduler::runReady> readyEvent; 164 void scheduleReadyEvent(); 165 166 uint64_t _numCycles; 167 168 Process *_current; 169 170 bool initReady; 171 172 ProcessList initList; 173 ProcessList toFinalize; 174 ProcessList readyList; 175 176 ChannelList updateList; 177}; 178 179extern Scheduler scheduler; 180 181} // namespace sc_gem5 182 183#endif // __SYSTEMC_CORE_SCHEDULER_H__ 184