src/cpu/activity.hh

   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/trace.hh"
  35 #include "cpu/timebuf.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  */
  52 class ActivityRecorder
  53 {
  54   public:
  55     ActivityRecorder(const std::string &name, int num_stages,
  56                      int longest_latency, int count);
  57     ~ActivityRecorder();
  58
  59     /** Records that there is activity this cycle. */
  60     void activity();
  61
  62     /** Advances the activity buffer, decrementing the activityCount
  63      *  if active communication just left the time buffer, and
  64      *  determining if there is no activity.
  65      */
  66     void advance();
  67
  68     /** Marks a stage as active. */
  69     void activateStage(const int idx);
  70
  71     /** Deactivates a stage. */
  72     void deactivateStage(const int idx);
  73
  74     /** Returns how many things are active within the recorder. */
  75     int getActivityCount() { return activityCount; }
  76
  77     /** Sets the count to a starting value.  Can be used to disable
  78      * the idling option.
  79      */
  80     void setActivityCount(int count)
  81     { activityCount = count; }
  82
  83     /** Returns if the CPU should be active. */
  84     bool active() { return activityCount; }
  85
  86     /** Clears the time buffer and the activity count. */
  87     void reset();
  88
  89     /** Debug function to dump the contents of the time buffer. */
  90     void dump();
  91
  92     /** Debug function to ensure that the activity count matches the
  93      * contents of the time buffer.
  94      */
  95     void validate();
  96
  97   private:
  98     // provide name() for DPRINTF.
  99     std::string _name;
 100     const std::string &name() { return _name; }
 101
 102     /** Time buffer that tracks if any cycles has active communication
 103      *  in them.  It should be as long as the longest communication
 104      *  latency in the system.  Each time any time buffer is written,
 105      *  the activity buffer should also be written to. The
 106      *  activityBuffer is advanced along with all the other time
 107      *  buffers, so it should have a 1 somewhere in it only if there
 108      *  is active communication in a time buffer.
 109      */
 110     TimeBuffer<bool> activityBuffer;
 111
 112     /** Longest latency time buffer in the CPU. */
 113     int longestLatency;
 114
 115     /** Tracks how many stages and cycles of time buffer have
 116      *  activity. Stages increment this count when they switch to
 117      *  active, and decrement it when they switch to
 118      *  inactive. Whenever a cycle that previously had no information
 119      *  is written in the time buffer, this is incremented. When a
 120      *  cycle that had information exits the time buffer due to age,
 121      *  this count is decremented. When the count is 0, there is no
 122      *  activity in the CPU, and it can be descheduled.
 123      */
 124     int activityCount;
 125
 126     /** Number of stages that can be marked as active or inactive. */
 127     int numStages;
 128
 129     /** Records which stages are active/inactive. */
 130     bool *stageActive;
 131 };
 132
 133 #endif // __CPU_ACTIVITY_HH__