activity.hh revision 2689 
1/*
2 * Copyright (c) 2006 The Regents of The University of Michigan
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions are
7 * met: redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer;
9 * redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution;
12 * neither the name of the copyright holders nor the names of its
13 * contributors may be used to endorse or promote products derived from
14 * this software without specific prior written permission.
15 *
16 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
17 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
18 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
19 * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
20 * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
21 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
22 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
26 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 *
28 * Authors: Kevin Lim
29 */
30
31#ifndef __CPU_ACTIVITY_HH__
32#define __CPU_ACTIVITY_HH__
33
34#include "base/timebuf.hh"
35#include "base/trace.hh"
36
37/**
38 * ActivityRecorder helper class that informs the CPU if it can switch
39 * over to being idle or not.  It works by having a time buffer as
40 * long as any time buffer in the CPU, and the CPU and all of its
41 * stages inform the ActivityRecorder when they write to any time
42 * buffer.  The ActivityRecorder marks a 1 in the "0" slot of the time
43 * buffer any time a stage writes to a time buffer, and it advances
44 * its time buffer at the same time as all other stages.  The
45 * ActivityRecorder also records if a stage has activity to do next
46 * cycle.  The recorder keeps a count of these two.  Thus any time the
47 * count is non-zero, there is either communication still in flight,
48 * or activity that still must be done, meaning that the CPU can not
49 * idle.  If count is zero, then the CPU can safely idle as it has no
50 * more outstanding work to do.
51 */
52class ActivityRecorder {
53  public:
54    ActivityRecorder(int num_stages, int longest_latency, int count);
55
56    /** Records that there is activity this cycle. */
57    void activity();
58
59    /** Advances the activity buffer, decrementing the activityCount
60     *  if active communication just left the time buffer, and
61     *  determining if there is no activity.
62     */
63    void advance();
64
65    /** Marks a stage as active. */
66    void activateStage(const int idx);
67
68    /** Deactivates a stage. */
69    void deactivateStage(const int idx);
70
71    /** Returns how many things are active within the recorder. */
72    int getActivityCount() { return activityCount; }
73
74    /** Sets the count to a starting value.  Can be used to disable
75     * the idling option.
76     */
77    void setActivityCount(int count)
78    { activityCount = count; }
79
80    /** Returns if the CPU should be active. */
81    bool active() { return activityCount; }
82
83    /** Clears the time buffer and the activity count. */
84    void reset();
85
86    /** Debug function to dump the contents of the time buffer. */
87    void dump();
88
89    /** Debug function to ensure that the activity count matches the
90     * contents of the time buffer.
91     */
92    void validate();
93
94  private:
95    /** Time buffer that tracks if any cycles has active communication
96     *  in them.  It should be as long as the longest communication
97     *  latency in the system.  Each time any time buffer is written,
98     *  the activity buffer should also be written to. The
99     *  activityBuffer is advanced along with all the other time
100     *  buffers, so it should have a 1 somewhere in it only if there
101     *  is active communication in a time buffer.
102     */
103    TimeBuffer<bool> activityBuffer;
104
105    /** Longest latency time buffer in the CPU. */
106    int longestLatency;
107
108    /** Tracks how many stages and cycles of time buffer have
109     *  activity. Stages increment this count when they switch to
110     *  active, and decrement it when they switch to
111     *  inactive. Whenever a cycle that previously had no information
112     *  is written in the time buffer, this is incremented. When a
113     *  cycle that had information exits the time buffer due to age,
114     *  this count is decremented. When the count is 0, there is no
115     *  activity in the CPU, and it can be descheduled.
116     */
117    int activityCount;
118
119    /** Number of stages that can be marked as active or inactive. */
120    int numStages;
121
122    /** Records which stages are active/inactive. */
123    bool *stageActive;
124};
125
126#endif // __CPU_ACTIVITY_HH__
127