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 __BASE_FAST_ALLOC_HH__
  38 #define __BASE_FAST_ALLOC_HH__
  39
  40 #include <cstddef>
  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
  75 #else
  76
  77 #if FAST_ALLOC_DEBUG
  78 #include "base/types.hh"
  79 #endif
  80
  81 class FastAlloc
  82 {
  83   public:
  84     static void *allocate(size_t);
  85     static void deallocate(void *, size_t);
  86
  87     void *operator new(size_t);
  88     void operator delete(void *, size_t);
  89
  90 #if FAST_ALLOC_DEBUG
  91     FastAlloc();
  92     FastAlloc(FastAlloc *, FastAlloc *);   // for inUseHead, see below
  93     virtual ~FastAlloc();
  94 #else
  95     virtual ~FastAlloc() {}
  96 #endif
  97
  98   private:
  99
 100     // Max_Alloc_Size is the largest object that can be allocated with
 101     // this class.  There's no fundamental limit, but this limits the
 102     // size of the freeLists array.  Let's not make this really huge
 103     // like in Blizzard.
 104     static const size_t Max_Alloc_Size = 512;
 105
 106     // Alloc_Quantum is the difference in size between adjacent
 107     // buckets in the free list array.
 108     static const int Log2_Alloc_Quantum = 3;
 109     static const int Alloc_Quantum = (1 << Log2_Alloc_Quantum);
 110
 111     // Num_Buckets = bucketFor(Max_Alloc_Size) + 1
 112     static const int Num_Buckets =
 113         ((Max_Alloc_Size + Alloc_Quantum - 1) >> Log2_Alloc_Quantum) + 1;
 114
 115     // when we call new() for more structures, how many should we get?
 116     static const int Num_Structs_Per_New = 20;
 117
 118     static int bucketFor(size_t);
 119     static void *moreStructs(int bucket);
 120
 121     static void *freeLists[Num_Buckets];
 122
 123 #if FAST_ALLOC_STATS
 124     static unsigned newCount[Num_Buckets];
 125     static unsigned deleteCount[Num_Buckets];
 126     static unsigned allocCount[Num_Buckets];
 127 #endif
 128
 129 #if FAST_ALLOC_DEBUG
 130     // per-object debugging fields
 131     bool inUse;                 // in-use flag
 132     FastAlloc *inUsePrev;       // ptrs to build list of in-use objects
 133     FastAlloc *inUseNext;
 134     Tick whenAllocated;
 135
 136     // static (global) debugging vars
 137     static int numInUse;        // count in-use objects
 138     static FastAlloc inUseHead; // dummy head for list of in-use objects
 139
 140   public:
 141     // functions to dump debugging info (see fast_alloc.cc for C
 142     // versions that might be more agreeable to call from gdb)
 143     static void dump_summary();
 144     static void dump_oldest(int n);
 145     static void dump_oldest_of_type(int n, const char *type_name);
 146 #endif
 147 };
 148
 149 inline int
 150 FastAlloc::bucketFor(size_t sz)
 151 {
 152     return (sz + Alloc_Quantum - 1) >> Log2_Alloc_Quantum;
 153 }
 154
 155 inline void *
 156 FastAlloc::allocate(size_t sz)
 157 {
 158     int b;
 159     void *p;
 160
 161     if (sz > Max_Alloc_Size)
 162         return (void *)::new char[sz];
 163
 164     b = bucketFor(sz);
 165     p = freeLists[b];
 166
 167     if (p)
 168         freeLists[b] = *(void **)p;
 169     else
 170         p = moreStructs(b);
 171
 172 #if FAST_ALLOC_STATS
 173     ++newCount[b];
 174 #endif
 175
 176     return p;
 177 }
 178
 179 inline void
 180 FastAlloc::deallocate(void *p, size_t sz)
 181 {
 182     int b;
 183
 184     if (sz > Max_Alloc_Size) {
 185         ::delete [] (char *)p;
 186         return;
 187     }
 188
 189     b = bucketFor(sz);
 190     *(void **)p = freeLists[b];
 191     freeLists[b] = p;
 192 #if FAST_ALLOC_STATS
 193     ++deleteCount[b];
 194 #endif
 195 }
 196
 197 inline void *
 198 FastAlloc::operator new(size_t sz)
 199 {
 200     return allocate(sz);
 201 }
 202
 203 inline void
 204 FastAlloc::operator delete(void *p, size_t sz)
 205 {
 206     deallocate(p, sz);
 207 }
 208
 209 #endif // NO_FAST_ALLOC
 210
 211 #endif // __BASE_FAST_ALLOC_HH__