src/cpu/x86/vm/vm_version_x86.hpp

Wed, 14 Dec 2011 14:54:38 -0800

author
kvn
date
Wed, 14 Dec 2011 14:54:38 -0800
changeset 3388
127b3692c168
parent 3063
9f12ede5571a
child 3400
22cee0ee8927
permissions
-rw-r--r--

7116452: Add support for AVX instructions
Summary: Added support for AVX extension to the x86 instruction set.
Reviewed-by: never

     1 /*
     2  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.
     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
     4  *
     5  * This code is free software; you can redistribute it and/or modify it
     6  * under the terms of the GNU General Public License version 2 only, as
     7  * published by the Free Software Foundation.
     8  *
     9  * This code is distributed in the hope that it will be useful, but WITHOUT
    10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    12  * version 2 for more details (a copy is included in the LICENSE file that
    13  * accompanied this code).
    14  *
    15  * You should have received a copy of the GNU General Public License version
    16  * 2 along with this work; if not, write to the Free Software Foundation,
    17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
    18  *
    19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
    20  * or visit www.oracle.com if you need additional information or have any
    21  * questions.
    22  *
    23  */
    25 #ifndef CPU_X86_VM_VM_VERSION_X86_HPP
    26 #define CPU_X86_VM_VM_VERSION_X86_HPP
    28 #include "runtime/globals_extension.hpp"
    29 #include "runtime/vm_version.hpp"
    31 class VM_Version : public Abstract_VM_Version {
    32 public:
    33   // cpuid result register layouts.  These are all unions of a uint32_t
    34   // (in case anyone wants access to the register as a whole) and a bitfield.
    36   union StdCpuid1Eax {
    37     uint32_t value;
    38     struct {
    39       uint32_t stepping   : 4,
    40                model      : 4,
    41                family     : 4,
    42                proc_type  : 2,
    43                           : 2,
    44                ext_model  : 4,
    45                ext_family : 8,
    46                           : 4;
    47     } bits;
    48   };
    50   union StdCpuid1Ebx { // example, unused
    51     uint32_t value;
    52     struct {
    53       uint32_t brand_id         : 8,
    54                clflush_size     : 8,
    55                threads_per_cpu  : 8,
    56                apic_id          : 8;
    57     } bits;
    58   };
    60   union StdCpuid1Ecx {
    61     uint32_t value;
    62     struct {
    63       uint32_t sse3     : 1,
    64                         : 2,
    65                monitor  : 1,
    66                         : 1,
    67                vmx      : 1,
    68                         : 1,
    69                est      : 1,
    70                         : 1,
    71                ssse3    : 1,
    72                cid      : 1,
    73                         : 2,
    74                cmpxchg16: 1,
    75                         : 4,
    76                dca      : 1,
    77                sse4_1   : 1,
    78                sse4_2   : 1,
    79                         : 2,
    80                popcnt   : 1,
    81                         : 3,
    82                osxsave  : 1,
    83                avx      : 1,
    84                         : 3;
    85     } bits;
    86   };
    88   union StdCpuid1Edx {
    89     uint32_t value;
    90     struct {
    91       uint32_t          : 4,
    92                tsc      : 1,
    93                         : 3,
    94                cmpxchg8 : 1,
    95                         : 6,
    96                cmov     : 1,
    97                         : 3,
    98                clflush  : 1,
    99                         : 3,
   100                mmx      : 1,
   101                fxsr     : 1,
   102                sse      : 1,
   103                sse2     : 1,
   104                         : 1,
   105                ht       : 1,
   106                         : 3;
   107     } bits;
   108   };
   110   union DcpCpuid4Eax {
   111     uint32_t value;
   112     struct {
   113       uint32_t cache_type    : 5,
   114                              : 21,
   115                cores_per_cpu : 6;
   116     } bits;
   117   };
   119   union DcpCpuid4Ebx {
   120     uint32_t value;
   121     struct {
   122       uint32_t L1_line_size  : 12,
   123                partitions    : 10,
   124                associativity : 10;
   125     } bits;
   126   };
   128   union TplCpuidBEbx {
   129     uint32_t value;
   130     struct {
   131       uint32_t logical_cpus : 16,
   132                             : 16;
   133     } bits;
   134   };
   136   union ExtCpuid1Ecx {
   137     uint32_t value;
   138     struct {
   139       uint32_t LahfSahf     : 1,
   140                CmpLegacy    : 1,
   141                             : 4,
   142                lzcnt        : 1,
   143                sse4a        : 1,
   144                misalignsse  : 1,
   145                prefetchw    : 1,
   146                             : 22;
   147     } bits;
   148   };
   150   union ExtCpuid1Edx {
   151     uint32_t value;
   152     struct {
   153       uint32_t           : 22,
   154                mmx_amd   : 1,
   155                mmx       : 1,
   156                fxsr      : 1,
   157                          : 4,
   158                long_mode : 1,
   159                tdnow2    : 1,
   160                tdnow     : 1;
   161     } bits;
   162   };
   164   union ExtCpuid5Ex {
   165     uint32_t value;
   166     struct {
   167       uint32_t L1_line_size : 8,
   168                L1_tag_lines : 8,
   169                L1_assoc     : 8,
   170                L1_size      : 8;
   171     } bits;
   172   };
   174   union ExtCpuid8Ecx {
   175     uint32_t value;
   176     struct {
   177       uint32_t cores_per_cpu : 8,
   178                              : 24;
   179     } bits;
   180   };
   182   union SefCpuid7Eax {
   183     uint32_t value;
   184   };
   186   union SefCpuid7Ebx {
   187     uint32_t value;
   188     struct {
   189       uint32_t fsgsbase : 1,
   190                         : 2,
   191                    bmi1 : 1,
   192                         : 1,
   193                    avx2 : 1,
   194                         : 2,
   195                    bmi2 : 1,
   196                         : 23;
   197     } bits;
   198   };
   200   union XemXcr0Eax {
   201     uint32_t value;
   202     struct {
   203       uint32_t x87 : 1,
   204                sse : 1,
   205                ymm : 1,
   206                    : 29;
   207     } bits;
   208   };
   210 protected:
   211    static int _cpu;
   212    static int _model;
   213    static int _stepping;
   214    static int _cpuFeatures;     // features returned by the "cpuid" instruction
   215                                 // 0 if this instruction is not available
   216    static const char* _features_str;
   218    enum {
   219      CPU_CX8    = (1 << 0), // next bits are from cpuid 1 (EDX)
   220      CPU_CMOV   = (1 << 1),
   221      CPU_FXSR   = (1 << 2),
   222      CPU_HT     = (1 << 3),
   223      CPU_MMX    = (1 << 4),
   224      CPU_3DNOW_PREFETCH  = (1 << 5), // Processor supports 3dnow prefetch and prefetchw instructions
   225                                      // may not necessarily support other 3dnow instructions
   226      CPU_SSE    = (1 << 6),
   227      CPU_SSE2   = (1 << 7),
   228      CPU_SSE3   = (1 << 8), // SSE3 comes from cpuid 1 (ECX)
   229      CPU_SSSE3  = (1 << 9),
   230      CPU_SSE4A  = (1 << 10),
   231      CPU_SSE4_1 = (1 << 11),
   232      CPU_SSE4_2 = (1 << 12),
   233      CPU_POPCNT = (1 << 13),
   234      CPU_LZCNT  = (1 << 14),
   235      CPU_AVX    = (1 << 15),
   236      CPU_AVX2   = (1 << 16)
   237    } cpuFeatureFlags;
   239   // cpuid information block.  All info derived from executing cpuid with
   240   // various function numbers is stored here.  Intel and AMD info is
   241   // merged in this block: accessor methods disentangle it.
   242   //
   243   // The info block is laid out in subblocks of 4 dwords corresponding to
   244   // eax, ebx, ecx and edx, whether or not they contain anything useful.
   245   struct CpuidInfo {
   246     // cpuid function 0
   247     uint32_t std_max_function;
   248     uint32_t std_vendor_name_0;
   249     uint32_t std_vendor_name_1;
   250     uint32_t std_vendor_name_2;
   252     // cpuid function 1
   253     StdCpuid1Eax std_cpuid1_eax;
   254     StdCpuid1Ebx std_cpuid1_ebx;
   255     StdCpuid1Ecx std_cpuid1_ecx;
   256     StdCpuid1Edx std_cpuid1_edx;
   258     // cpuid function 4 (deterministic cache parameters)
   259     DcpCpuid4Eax dcp_cpuid4_eax;
   260     DcpCpuid4Ebx dcp_cpuid4_ebx;
   261     uint32_t     dcp_cpuid4_ecx; // unused currently
   262     uint32_t     dcp_cpuid4_edx; // unused currently
   264     // cpuid function 7 (structured extended features)
   265     SefCpuid7Eax sef_cpuid7_eax;
   266     SefCpuid7Ebx sef_cpuid7_ebx;
   267     uint32_t     sef_cpuid7_ecx; // unused currently
   268     uint32_t     sef_cpuid7_edx; // unused currently
   270     // cpuid function 0xB (processor topology)
   271     // ecx = 0
   272     uint32_t     tpl_cpuidB0_eax;
   273     TplCpuidBEbx tpl_cpuidB0_ebx;
   274     uint32_t     tpl_cpuidB0_ecx; // unused currently
   275     uint32_t     tpl_cpuidB0_edx; // unused currently
   277     // ecx = 1
   278     uint32_t     tpl_cpuidB1_eax;
   279     TplCpuidBEbx tpl_cpuidB1_ebx;
   280     uint32_t     tpl_cpuidB1_ecx; // unused currently
   281     uint32_t     tpl_cpuidB1_edx; // unused currently
   283     // ecx = 2
   284     uint32_t     tpl_cpuidB2_eax;
   285     TplCpuidBEbx tpl_cpuidB2_ebx;
   286     uint32_t     tpl_cpuidB2_ecx; // unused currently
   287     uint32_t     tpl_cpuidB2_edx; // unused currently
   289     // cpuid function 0x80000000 // example, unused
   290     uint32_t ext_max_function;
   291     uint32_t ext_vendor_name_0;
   292     uint32_t ext_vendor_name_1;
   293     uint32_t ext_vendor_name_2;
   295     // cpuid function 0x80000001
   296     uint32_t     ext_cpuid1_eax; // reserved
   297     uint32_t     ext_cpuid1_ebx; // reserved
   298     ExtCpuid1Ecx ext_cpuid1_ecx;
   299     ExtCpuid1Edx ext_cpuid1_edx;
   301     // cpuid functions 0x80000002 thru 0x80000004: example, unused
   302     uint32_t proc_name_0, proc_name_1, proc_name_2, proc_name_3;
   303     uint32_t proc_name_4, proc_name_5, proc_name_6, proc_name_7;
   304     uint32_t proc_name_8, proc_name_9, proc_name_10,proc_name_11;
   306     // cpuid function 0x80000005 //AMD L1, Intel reserved
   307     uint32_t     ext_cpuid5_eax; // unused currently
   308     uint32_t     ext_cpuid5_ebx; // reserved
   309     ExtCpuid5Ex  ext_cpuid5_ecx; // L1 data cache info (AMD)
   310     ExtCpuid5Ex  ext_cpuid5_edx; // L1 instruction cache info (AMD)
   312     // cpuid function 0x80000008
   313     uint32_t     ext_cpuid8_eax; // unused currently
   314     uint32_t     ext_cpuid8_ebx; // reserved
   315     ExtCpuid8Ecx ext_cpuid8_ecx;
   316     uint32_t     ext_cpuid8_edx; // reserved
   318     // extended control register XCR0 (the XFEATURE_ENABLED_MASK register)
   319     XemXcr0Eax   xem_xcr0_eax;
   320     uint32_t     xem_xcr0_edx; // reserved
   321   };
   323   // The actual cpuid info block
   324   static CpuidInfo _cpuid_info;
   326   // Extractors and predicates
   327   static uint32_t extended_cpu_family() {
   328     uint32_t result = _cpuid_info.std_cpuid1_eax.bits.family;
   329     result += _cpuid_info.std_cpuid1_eax.bits.ext_family;
   330     return result;
   331   }
   332   static uint32_t extended_cpu_model() {
   333     uint32_t result = _cpuid_info.std_cpuid1_eax.bits.model;
   334     result |= _cpuid_info.std_cpuid1_eax.bits.ext_model << 4;
   335     return result;
   336   }
   337   static uint32_t cpu_stepping() {
   338     uint32_t result = _cpuid_info.std_cpuid1_eax.bits.stepping;
   339     return result;
   340   }
   341   static uint logical_processor_count() {
   342     uint result = threads_per_core();
   343     return result;
   344   }
   345   static uint32_t feature_flags() {
   346     uint32_t result = 0;
   347     if (_cpuid_info.std_cpuid1_edx.bits.cmpxchg8 != 0)
   348       result |= CPU_CX8;
   349     if (_cpuid_info.std_cpuid1_edx.bits.cmov != 0)
   350       result |= CPU_CMOV;
   351     if (_cpuid_info.std_cpuid1_edx.bits.fxsr != 0 || (is_amd() &&
   352         _cpuid_info.ext_cpuid1_edx.bits.fxsr != 0))
   353       result |= CPU_FXSR;
   354     // HT flag is set for multi-core processors also.
   355     if (threads_per_core() > 1)
   356       result |= CPU_HT;
   357     if (_cpuid_info.std_cpuid1_edx.bits.mmx != 0 || (is_amd() &&
   358         _cpuid_info.ext_cpuid1_edx.bits.mmx != 0))
   359       result |= CPU_MMX;
   360     if (_cpuid_info.std_cpuid1_edx.bits.sse != 0)
   361       result |= CPU_SSE;
   362     if (_cpuid_info.std_cpuid1_edx.bits.sse2 != 0)
   363       result |= CPU_SSE2;
   364     if (_cpuid_info.std_cpuid1_ecx.bits.sse3 != 0)
   365       result |= CPU_SSE3;
   366     if (_cpuid_info.std_cpuid1_ecx.bits.ssse3 != 0)
   367       result |= CPU_SSSE3;
   368     if (_cpuid_info.std_cpuid1_ecx.bits.sse4_1 != 0)
   369       result |= CPU_SSE4_1;
   370     if (_cpuid_info.std_cpuid1_ecx.bits.sse4_2 != 0)
   371       result |= CPU_SSE4_2;
   372     if (_cpuid_info.std_cpuid1_ecx.bits.popcnt != 0)
   373       result |= CPU_POPCNT;
   374     if (_cpuid_info.std_cpuid1_ecx.bits.avx != 0 &&
   375         _cpuid_info.std_cpuid1_ecx.bits.osxsave != 0 &&
   376         _cpuid_info.xem_xcr0_eax.bits.sse != 0 &&
   377         _cpuid_info.xem_xcr0_eax.bits.ymm != 0) {
   378       result |= CPU_AVX;
   379       if (_cpuid_info.sef_cpuid7_ebx.bits.avx2 != 0)
   380         result |= CPU_AVX2;
   381     }
   383     // AMD features.
   384     if (is_amd()) {
   385       if ((_cpuid_info.ext_cpuid1_edx.bits.tdnow != 0) ||
   386           (_cpuid_info.ext_cpuid1_ecx.bits.prefetchw != 0))
   387         result |= CPU_3DNOW_PREFETCH;
   388       if (_cpuid_info.ext_cpuid1_ecx.bits.lzcnt != 0)
   389         result |= CPU_LZCNT;
   390       if (_cpuid_info.ext_cpuid1_ecx.bits.sse4a != 0)
   391         result |= CPU_SSE4A;
   392     }
   394     return result;
   395   }
   397   static void get_processor_features();
   399 public:
   400   // Offsets for cpuid asm stub
   401   static ByteSize std_cpuid0_offset() { return byte_offset_of(CpuidInfo, std_max_function); }
   402   static ByteSize std_cpuid1_offset() { return byte_offset_of(CpuidInfo, std_cpuid1_eax); }
   403   static ByteSize dcp_cpuid4_offset() { return byte_offset_of(CpuidInfo, dcp_cpuid4_eax); }
   404   static ByteSize sef_cpuid7_offset() { return byte_offset_of(CpuidInfo, sef_cpuid7_eax); }
   405   static ByteSize ext_cpuid1_offset() { return byte_offset_of(CpuidInfo, ext_cpuid1_eax); }
   406   static ByteSize ext_cpuid5_offset() { return byte_offset_of(CpuidInfo, ext_cpuid5_eax); }
   407   static ByteSize ext_cpuid8_offset() { return byte_offset_of(CpuidInfo, ext_cpuid8_eax); }
   408   static ByteSize tpl_cpuidB0_offset() { return byte_offset_of(CpuidInfo, tpl_cpuidB0_eax); }
   409   static ByteSize tpl_cpuidB1_offset() { return byte_offset_of(CpuidInfo, tpl_cpuidB1_eax); }
   410   static ByteSize tpl_cpuidB2_offset() { return byte_offset_of(CpuidInfo, tpl_cpuidB2_eax); }
   411   static ByteSize xem_xcr0_offset() { return byte_offset_of(CpuidInfo, xem_xcr0_eax); }
   413   // Initialization
   414   static void initialize();
   416   // Asserts
   417   static void assert_is_initialized() {
   418     assert(_cpuid_info.std_cpuid1_eax.bits.family != 0, "VM_Version not initialized");
   419   }
   421   //
   422   // Processor family:
   423   //       3   -  386
   424   //       4   -  486
   425   //       5   -  Pentium
   426   //       6   -  PentiumPro, Pentium II, Celeron, Xeon, Pentium III, Athlon,
   427   //              Pentium M, Core Solo, Core Duo, Core2 Duo
   428   //    family 6 model:   9,        13,       14,        15
   429   //    0x0f   -  Pentium 4, Opteron
   430   //
   431   // Note: The cpu family should be used to select between
   432   //       instruction sequences which are valid on all Intel
   433   //       processors.  Use the feature test functions below to
   434   //       determine whether a particular instruction is supported.
   435   //
   436   static int  cpu_family()        { return _cpu;}
   437   static bool is_P6()             { return cpu_family() >= 6; }
   439   static bool is_amd()            { assert_is_initialized(); return _cpuid_info.std_vendor_name_0 == 0x68747541; } // 'htuA'
   440   static bool is_intel()          { assert_is_initialized(); return _cpuid_info.std_vendor_name_0 == 0x756e6547; } // 'uneG'
   442   static bool supports_processor_topology() {
   443     return (_cpuid_info.std_max_function >= 0xB) &&
   444            // eax[4:0] | ebx[0:15] == 0 indicates invalid topology level.
   445            // Some cpus have max cpuid >= 0xB but do not support processor topology.
   446            ((_cpuid_info.tpl_cpuidB0_eax & 0x1f | _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus) != 0);
   447   }
   449   static uint cores_per_cpu()  {
   450     uint result = 1;
   451     if (is_intel()) {
   452       if (supports_processor_topology()) {
   453         result = _cpuid_info.tpl_cpuidB1_ebx.bits.logical_cpus /
   454                  _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus;
   455       } else {
   456         result = (_cpuid_info.dcp_cpuid4_eax.bits.cores_per_cpu + 1);
   457       }
   458     } else if (is_amd()) {
   459       result = (_cpuid_info.ext_cpuid8_ecx.bits.cores_per_cpu + 1);
   460     }
   461     return result;
   462   }
   464   static uint threads_per_core()  {
   465     uint result = 1;
   466     if (is_intel() && supports_processor_topology()) {
   467       result = _cpuid_info.tpl_cpuidB0_ebx.bits.logical_cpus;
   468     } else if (_cpuid_info.std_cpuid1_edx.bits.ht != 0) {
   469       result = _cpuid_info.std_cpuid1_ebx.bits.threads_per_cpu /
   470                cores_per_cpu();
   471     }
   472     return result;
   473   }
   475   static intx prefetch_data_size()  {
   476     intx result = 0;
   477     if (is_intel()) {
   478       result = (_cpuid_info.dcp_cpuid4_ebx.bits.L1_line_size + 1);
   479     } else if (is_amd()) {
   480       result = _cpuid_info.ext_cpuid5_ecx.bits.L1_line_size;
   481     }
   482     if (result < 32) // not defined ?
   483       result = 32;   // 32 bytes by default on x86 and other x64
   484     return result;
   485   }
   487   //
   488   // Feature identification
   489   //
   490   static bool supports_cpuid()    { return _cpuFeatures  != 0; }
   491   static bool supports_cmpxchg8() { return (_cpuFeatures & CPU_CX8) != 0; }
   492   static bool supports_cmov()     { return (_cpuFeatures & CPU_CMOV) != 0; }
   493   static bool supports_fxsr()     { return (_cpuFeatures & CPU_FXSR) != 0; }
   494   static bool supports_ht()       { return (_cpuFeatures & CPU_HT) != 0; }
   495   static bool supports_mmx()      { return (_cpuFeatures & CPU_MMX) != 0; }
   496   static bool supports_sse()      { return (_cpuFeatures & CPU_SSE) != 0; }
   497   static bool supports_sse2()     { return (_cpuFeatures & CPU_SSE2) != 0; }
   498   static bool supports_sse3()     { return (_cpuFeatures & CPU_SSE3) != 0; }
   499   static bool supports_ssse3()    { return (_cpuFeatures & CPU_SSSE3)!= 0; }
   500   static bool supports_sse4_1()   { return (_cpuFeatures & CPU_SSE4_1) != 0; }
   501   static bool supports_sse4_2()   { return (_cpuFeatures & CPU_SSE4_2) != 0; }
   502   static bool supports_popcnt()   { return (_cpuFeatures & CPU_POPCNT) != 0; }
   503   static bool supports_avx()      { return (_cpuFeatures & CPU_AVX) != 0; }
   504   static bool supports_avx2()     { return (_cpuFeatures & CPU_AVX2) != 0; }
   505   //
   506   // AMD features
   507   //
   508   static bool supports_3dnow_prefetch()    { return (_cpuFeatures & CPU_3DNOW_PREFETCH) != 0; }
   509   static bool supports_mmx_ext()  { return is_amd() && _cpuid_info.ext_cpuid1_edx.bits.mmx_amd != 0; }
   510   static bool supports_lzcnt()    { return (_cpuFeatures & CPU_LZCNT) != 0; }
   511   static bool supports_sse4a()    { return (_cpuFeatures & CPU_SSE4A) != 0; }
   513   // Intel Core and newer cpus have fast IDIV instruction (excluding Atom).
   514   static bool has_fast_idiv()     { return is_intel() && cpu_family() == 6 &&
   515                                            supports_sse3() && _model != 0x1C; }
   517   static bool supports_compare_and_exchange() { return true; }
   519   static const char* cpu_features()           { return _features_str; }
   521   static intx allocate_prefetch_distance() {
   522     // This method should be called before allocate_prefetch_style().
   523     //
   524     // Hardware prefetching (distance/size in bytes):
   525     // Pentium 3 -  64 /  32
   526     // Pentium 4 - 256 / 128
   527     // Athlon    -  64 /  32 ????
   528     // Opteron   - 128 /  64 only when 2 sequential cache lines accessed
   529     // Core      - 128 /  64
   530     //
   531     // Software prefetching (distance in bytes / instruction with best score):
   532     // Pentium 3 - 128 / prefetchnta
   533     // Pentium 4 - 512 / prefetchnta
   534     // Athlon    - 128 / prefetchnta
   535     // Opteron   - 256 / prefetchnta
   536     // Core      - 256 / prefetchnta
   537     // It will be used only when AllocatePrefetchStyle > 0
   539     intx count = AllocatePrefetchDistance;
   540     if (count < 0) {   // default ?
   541       if (is_amd()) {  // AMD
   542         if (supports_sse2())
   543           count = 256; // Opteron
   544         else
   545           count = 128; // Athlon
   546       } else {         // Intel
   547         if (supports_sse2())
   548           if (cpu_family() == 6) {
   549             count = 256; // Pentium M, Core, Core2
   550           } else {
   551             count = 512; // Pentium 4
   552           }
   553         else
   554           count = 128; // Pentium 3 (and all other old CPUs)
   555       }
   556     }
   557     return count;
   558   }
   559   static intx allocate_prefetch_style() {
   560     assert(AllocatePrefetchStyle >= 0, "AllocatePrefetchStyle should be positive");
   561     // Return 0 if AllocatePrefetchDistance was not defined.
   562     return AllocatePrefetchDistance > 0 ? AllocatePrefetchStyle : 0;
   563   }
   565   // Prefetch interval for gc copy/scan == 9 dcache lines.  Derived from
   566   // 50-warehouse specjbb runs on a 2-way 1.8ghz opteron using a 4gb heap.
   567   // Tested intervals from 128 to 2048 in increments of 64 == one cache line.
   568   // 256 bytes (4 dcache lines) was the nearest runner-up to 576.
   570   // gc copy/scan is disabled if prefetchw isn't supported, because
   571   // Prefetch::write emits an inlined prefetchw on Linux.
   572   // Do not use the 3dnow prefetchw instruction.  It isn't supported on em64t.
   573   // The used prefetcht0 instruction works for both amd64 and em64t.
   574   static intx prefetch_copy_interval_in_bytes() {
   575     intx interval = PrefetchCopyIntervalInBytes;
   576     return interval >= 0 ? interval : 576;
   577   }
   578   static intx prefetch_scan_interval_in_bytes() {
   579     intx interval = PrefetchScanIntervalInBytes;
   580     return interval >= 0 ? interval : 576;
   581   }
   582   static intx prefetch_fields_ahead() {
   583     intx count = PrefetchFieldsAhead;
   584     return count >= 0 ? count : 1;
   585   }
   586 };
   588 #endif // CPU_X86_VM_VM_VERSION_X86_HPP

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