src/base/fast_alloc.hh

   1 /*
   2  * Copyright (c) 2000-2001, 2003-2005 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: Steve Reinhardt
  29  */
  30
  31 /*
  32  * This code was originally written by Steve Reinhardt as part of
  33  * the Wisconsin Wind Tunnel simulator.  Relicensed as part of M5
  34  * by permission.
  35  */
  36
  37 #ifndef __FAST_ALLOC_H__
  38 #define __FAST_ALLOC_H__
  39
  40 #include <stddef.h>
  41
  42 // Fast structure allocator.  Designed for small objects that are
  43 // frequently allocated and deallocated.  This code is derived from the
  44 // 'alloc_struct' package used in WWT and Blizzard.  C++ provides a
  45 // much nicer framework for the same optimization.  The package is
  46 // implemented as a class, FastAlloc.  Allocation and deletion are
  47 // performed using FastAlloc's new and delete operators.  Any object
  48 // that derives from the FastAlloc class will transparently use this
  49 // allocation package.
  50
  51 // The static allocate() and deallocate() methods can also be called
  52 // directly if desired.
  53
  54 // In order for derived classes to call delete with the correct
  55 // structure size even when they are deallocated via a base-type
  56 // pointer, they must have a virtual destructor.  It is sufficient for
  57 // FastAlloc to declare a virtual destructor (as it does); it is not
  58 // required for derived classes to declare their own destructor.  The
  59 // compiler will automatically generate a virtual destructor for each
  60 // derived class.  However, it is more efficient if each derived class
  61 // defines an inline destructor, so that the compiler can statically
  62 // collapse the destructor call chain back up the inheritance
  63 // hierarchy.
  64
  65 #include "config/no_fast_alloc.hh"
  66 #include "config/fast_alloc_debug.hh"
  67 #include "config/fast_alloc_stats.hh"
  68
  69 #if NO_FAST_ALLOC
  70
  71 class FastAlloc {
  72 };
  73
  74 #else
  75
  76 class FastAlloc {
  77   public:
  78
  79     static void *allocate(size_t);
  80     static void deallocate(void *, size_t);
  81
  82     void *operator new(size_t);
  83     void operator delete(void *, size_t);
  84
  85 #if FAST_ALLOC_DEBUG
  86     FastAlloc();
  87     FastAlloc(FastAlloc*,FastAlloc*);   // for inUseHead, see below
  88     virtual ~FastAlloc();
  89 #else
  90     virtual ~FastAlloc() {}
  91 #endif
  92
  93   private:
  94
  95     // Max_Alloc_Size is the largest object that can be allocated with
  96     // this class.  There's no fundamental limit, but this limits the
  97     // size of the freeLists array.  Let's not make this really huge
  98     // like in Blizzard.
  99     static const int Max_Alloc_Size = 512;
 100
 101     // Alloc_Quantum is the difference in size between adjacent
 102     // buckets in the free list array.
 103     static const int Log2_Alloc_Quantum = 3;
 104     static const int Alloc_Quantum = (1 << Log2_Alloc_Quantum);
 105
 106     // Num_Buckets = bucketFor(Max_Alloc_Size) + 1
 107     static const int Num_Buckets =
 108         ((Max_Alloc_Size + Alloc_Quantum - 1) >> Log2_Alloc_Quantum) + 1;
 109
 110     // when we call new() for more structures, how many should we get?
 111     static const int Num_Structs_Per_New = 20;
 112
 113     static int bucketFor(size_t);
 114     static void *moreStructs(int bucket);
 115
 116     static void *freeLists[Num_Buckets];
 117
 118 #if FAST_ALLOC_STATS
 119     static unsigned newCount[Num_Buckets];
 120     static unsigned deleteCount[Num_Buckets];
 121     static unsigned allocCount[Num_Buckets];
 122 #endif
 123
 124 #if FAST_ALLOC_DEBUG
 125     // per-object debugging fields
 126     bool inUse;                 // in-use flag
 127     FastAlloc *inUsePrev;       // ptrs to build list of in-use objects
 128     FastAlloc *inUseNext;
 129
 130     // static (global) debugging vars
 131     static int numInUse;        // count in-use objects
 132     static FastAlloc inUseHead; // dummy head for list of in-use objects
 133
 134   public:
 135     // functions to dump debugging info (see fast_alloc.cc for C
 136     // versions that might be more agreeable to call from gdb)
 137     static void dump_summary();
 138     static void dump_oldest(int n);
 139 #endif
 140 };
 141
 142
 143 inline
 144 int FastAlloc::bucketFor(size_t sz)
 145 {
 146     return (sz + Alloc_Quantum - 1) >> Log2_Alloc_Quantum;
 147 }
 148
 149
 150 inline
 151 void *FastAlloc::allocate(size_t sz)
 152 {
 153     int b;
 154     void *p;
 155
 156     if (sz > Max_Alloc_Size)
 157         return (void *)::new char[sz];
 158
 159     b = bucketFor(sz);
 160     p = freeLists[b];
 161
 162     if (p)
 163         freeLists[b] = *(void **)p;
 164     else
 165         p = moreStructs(b);
 166
 167 #if FAST_ALLOC_STATS
 168     ++newCount[b];
 169 #endif
 170
 171     return p;
 172 }
 173
 174
 175 inline
 176 void FastAlloc::deallocate(void *p, size_t sz)
 177 {
 178     int b;
 179
 180     if (sz > Max_Alloc_Size)
 181     {
 182         ::delete [] (char *)p;
 183         return;
 184     }
 185
 186     b = bucketFor(sz);
 187     *(void **)p = freeLists[b];
 188     freeLists[b] = p;
 189 #if FAST_ALLOC_STATS
 190     ++deleteCount[b];
 191 #endif
 192 }
 193
 194
 195 inline
 196 void *FastAlloc::operator new(size_t sz)
 197 {
 198     return allocate(sz);
 199 }
 200
 201
 202 inline
 203 void FastAlloc::operator delete(void *p, size_t sz)
 204 {
 205     deallocate(p, sz);
 206 }
 207
 208 #endif // NO_FAST_ALLOC
 209
 210 #endif // __FAST_ALLOC_H__