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Performance/Reorder Symbols For Libraries

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The comprehensive analysis of the cold start up behavior of OpenOffice.org shows that file I/O is the main bottleneck. About 80% of the start up time is spent waiting for data from the disk. Most file I/O depends on library loading. This part describes what can be done to reduce I/O time for loading OpenOffice.org libraries. The main ideas are system independent but the solutions must be system/compiler specific. The following chapters describe in detail how we want to reorder code/data within the libraries.

Main idea

Normally the compiler and linker produce a library which consists of many object files. The order of the code/data is dependent on the strategy of the linker and the layout of the library format. During the start up the application libraries are loaded on demand. Dependend on the program flow new code and therefore pages are loaded from disk into memory. Unfortunately the linker doesn't know how the application accesses every library during the start up phase. Therefore the needed code/data is distributed all over the library which causes many page faults and disk access.

Main Idea Library Optimization.png

System dependent solution

Windows

This chapter describes the solution for the Windows platform.

Microsoft Visual Studio 2008

OpenOffice.org uses the Microsoft Visual Studio 2008 C/C++ compiler suite for the Windows build, called wntmsci12[.pro]. Unfortunately Microsoft discontinued the Working Set Tuner application which was part of the Platform SDK. That application allowed developers to optimize the layout of application libraries. A successor called Smooth Working Set Tool is also not available for download.

So we have to look for a solution on our own. This has also the big advantage that the solution can be adapted to our needs. What options are available to support us reordering code/data in libraries? If you start the C/C++ compiler and linker with the help option you can see all supported options. The following section shows the options which can help us.

Compiler options

Microsoft (R) 32-Bit C/C++-Optimizing Compiler Version 15.00.30729.01 for 80x86
 
Copyright (C) Microsoft Corporation.  All rights reserved.
 
...
/Gh Enable _penter function call        
/GH Enable _pexit function call
/Gy Enable Function-Level Linking
...
 
Microsoft (R) Incremental Linker Version 9.00.30729.01
Copyright (C) Microsoft Corporation.  All rights reserved.
 
 Syntax: LINK [Options] [Files] [@Commandfile]
 
   Options:
      ...
      /ORDER:@Filename
      ...

The /Gh compiler option provides us the ability to be called by every function entry. The call to the hook function will be added by the compiler. That means we have to rebuild all libraries that should be instrumented with the /Gh option set. The /GH option is useful if we want to measure timing therefore we don't need it for record function calls. The /Gy options is needed to reorder symbols by the linker. Fortunately this options is set on official OpenOffice.org builds.

Looking at the documentation for the /Gh option Microsoft states that the hook function must be declared as naked. The function must also preserve all register content.

void __declspec(naked) _cdecl _penter( void );

A function declared with the naked attribute doesn't have prolog or epilog code. It enables a developer to write his own custom prolog/epilog code using the inline assembler. The following skeleton can be used for our target to record all function calls during the start up.

extern "C" void __declspec(naked) _cdecl _penter( void )
{
   _asm
   {
      push eax
      push ebx
      push ecx
      push edx
      push ebp
      push edi
      push esi
   }
 
   // TODO: Add code to determine the caller address and provide it
   // to a function which records the call.
 
   _asm
   {
      pop esi
      pop edi
      pop ebp
      pop edx
      pop ecx
      pop ebx
      pop eax
      ret
   }
}

What we have to do is to retrieve the address of the caller function. This can be done with a little calculation as the address is on the stack. See the following code.

extern "C" void __declspec(naked) _cdecl _penter( void )
{
    _asm
    {
        push eax
        push ebx
        push ecx
        push edx
        push ebp
        push edi
        push esi
 
        // calculate the pointer to the return address
        mov  ecx, esp
        add  ecx, 28
 
        // retrieve return address from stack
        mov  eax, dword ptr[ecx]
 
        // subtract 5 bytes as instruction for call _penter is 5 bytes long on 32-bit machines, e.g. E8 <00 00 00 00>
        sub  eax, 5
 
        // provide return address to recordFunctionCall
        push eax
        call forwardFunctionCall
 
        pop esi
        pop edi
        pop ebp
        pop edx
        pop ecx
        pop ebx
        pop eax
        ret
    }
}

The implementation of the _penter function provides the start address of the called function to an external function which can be implemented by C++ code.

Determine what functions are called during start up

With the help of the _penter function we are able to get the function addresses which are called during the start up. The _penter function calls an second function which can be implemented using C++. The function has to implement the following tasks:

  • Determine to which module the address belongs

The order files for the linker must be created for every single library. We also need to know what map file must be checked later. It's not complicated to find the module to an address. The following code retrieves module information from a virtual address. The module information should be cached to minimize the overhead for the hook function, otherwise the runtime of the instrumented code can grow to an unacceptable amount.

bool getModuleDataFromAddress(void* pAddress, HMODULE* pModule, WCHAR* pszModuleName, DWORD dwBufSize, DWORD* dwModuleSize)
{
    // Determine current module name
    bool    bFound      = false;
    DWORD   dwProcessID = GetCurrentProcessId();
    HANDLE  hSnapshot   = CreateToolhelp32Snapshot( TH32CS_SNAPMODULE, dwProcessID );
    if (hSnapshot != INVALID_HANDLE_VALUE)
    {
        MODULEENTRY32 me32;
 
        me32.dwSize = sizeof( MODULEENTRY32 );
        if( Module32First( hSnapshot, &me32 ) ) 
        { 
            do
            {
                BYTE* pModuleBaseAddress = me32.modBaseAddr;
                DWORD dwSize             = me32.modBaseSize;
                if ( pAddress >= pModuleBaseAddress && pAddress <= ( pModuleBaseAddress + dwSize ))
                {
                    bFound        = true;
                    *pModule      = me32.hModule;
                    *dwModuleSize = dwSize;
                    wcsncpy( pszModuleName, me32.szModule, dwBufSize);
                    break;
                }
            }
            while( Module32Next( hSnapshot, &me32 ) ); 
        }
        CloseHandle(hSnapshot);
    }
 
    return bFound;
}
  • Control a counter for every module which tags every new detected function with the current count. This gives us the opportunity to sort the function symbols related to their call sequence.
  • An access counter for every function to give us a chance to sort the function symbols related to their importance.
  • The trace code must be able to write the collected information into a trace file which can be processed later.

It's clear that the implementation of this record function should be optimized as it is called many times (therefore this is time critical).

How to create an ORDER file that is accepted by the linker

There is no real documentation about the decoration schema Microsoft uses for their C++ compilers. A very comprehensive description can be found on the following Wikipedia page: http://en.wikipedia.org/wiki/Microsoft_Visual_C%2B%2B_Name_Mangling.

A second tool can create with the trace file and the map file an order file. The map reveals the symbol for an address and the size of the function can be calculated. Dependent on the sort algorithm the order can be written for the instrumented modules.

Use the map file information to map an address to a symbol

These information must be stored into trace files that can be analyzed by an additional tool. This tool will use the modules map file to determine the symbol from the address and it can also detect if the symbol is static or not. Static symbols cannot be moved by the linker.

Snippet from a typical map file
 splmi
 
 Timestamp is 49cce429 (Fri Mar 27 15:35:21 2009)
 
 Preferred load address is 10000000
 
 Start         Length     Name                   Class
 0001:00000000 0001266aH .text                   CODE
 0001:00012670 00003e58H .text$x                 CODE
 0001:000164d0 0000010cH .text$yc                CODE
 0001:000165e0 000000d3H .text$yd                CODE
 0002:00000000 000007c0H .idata$5                DATA
 0002:000007c0 00000004H .CRT$XCA                DATA
 0002:000007c4 0000001cH .CRT$XCU                DATA
 0002:000007e0 00000004H .CRT$XCZ                DATA
 0002:000007e4 00000004H .CRT$XIA                DATA
 0002:000007e8 00000004H .CRT$XIAA               DATA
 0002:000007ec 00000004H .CRT$XIC                DATA
 0002:000007f0 00000004H .CRT$XIZ                DATA
 0002:00000800 00001bf8H .rdata                  DATA
 0002:000023f8 0000004dH .rdata$debug            DATA
 0002:00002448 000013d8H .rdata$r                DATA
 0002:00003820 0000038cH .rdata$sxdata           DATA
 0002:00003bac 00000004H .rtc$IAA                DATA
 0002:00003bb0 00000004H .rtc$IZZ                DATA
 0002:00003bb4 00000004H .rtc$TAA                DATA
 0002:00003bb8 00000004H .rtc$TZZ                DATA
 0002:00003bc0 000044acH .xdata$x                DATA
 0002:0000806c 0000012cH .idata$2                DATA
 0002:00008198 00000014H .idata$3                DATA
 0002:000081ac 000007c0H .idata$4                DATA
 0002:0000896c 00004fc4H .idata$6                DATA
 0002:0000d930 000000b9H .edata                  DATA
 0003:00000000 000009e8H .data                   DATA
 0003:000009e8 00000418H .bss                    DATA
 0004:00000000 000000ecH .rsrc$01                DATA
 0004:000000f0 00000278H .rsrc$02                DATA
 
  Address         Publics by Value              Rva+Base       Lib:Object
 
 0000:00000000       __except_list              00000000     <absolute>
 0000:000000e3       ___safe_se_handler_count   000000e3     <absolute>
 0000:00009876       __ldused                   00009876     <absolute>
 0000:00009876       __fltused                  00009876     <absolute>
 0000:00000000       ___ImageBase               10000000     <linker-defined>
 0001:00000000       ??0SplashScreen@desktop@@AAE@ABV?$Reference@VXMultiServiceFactory@lang@star@sun@com@@@uno@star@sun@com@@@Z 10001000 f   splash.obj
 0001:000002e0       ??1OUString@rtl@@QAE@XZ    100012e0 f i splash.obj
 0001:00000300       ??_GSplashScreen@desktop@@EAEPAXI@Z 10001300 f i splash.obj
 0001:00000300       ??_ESplashScreen@desktop@@EAEPAXI@Z 10001300 f i splash.obj
 0001:00000340       ??1?$WeakImplHelper2@VXStatusIndicator@task@star@sun@com@@VXInitialization@lang@345@@cppu@@UAE@XZ 10001340 f i splash.obj
 0001:00000390       ??1SplashScreen@desktop@@EAE@XZ 10001390 f   splash.obj
 0001:000004d0       ?start@SplashScreen@desktop@@UAAXABVOUString@rtl@@J@Z 100014d0 f   splash.obj
 0001:000005d0       ??1OGuard@vos@@UAE@XZ      100015d0 f i splash.obj
 0001:00000600       ??_GOGuard@vos@@UAEPAXI@Z  10001600 f i splash.obj
 0001:00000600       ??_EOGuard@vos@@UAEPAXI@Z  10001600 f i splash.obj
 0001:00000650       ?end@SplashScreen@desktop@@UAAXXZ 10001650 f   splash.obj
 ...
 
 entry point at        0001:00012246
 
 Static symbols
 
 0001:fffff000       __unwindfunclet$?copy@OUString@rtl@@QBE?AV12@JJ@Z$0 10000000 f   cfgfilter.obj
 0001:fffff000       __unwindfunclet$??0Exception@uno@star@sun@com@@QAE@ABVOUString@rtl@@ABV?$Reference@VXInterface@uno@star@sun@com@@@1234@@Z$0 10000000 f   migration.obj
 ...
 0001:000164ad       __ehhandler$?overrideProperty@CConfigFilter@desktop@@UAAXABVOUString@rtl@@FABVType@uno@star@sun@com@@E@Z 100174ad f   cfgfilter.obj
 0001:000164d0       ??__E?_aMutex@SplashScreen@desktop@@0VMutex@osl@@A@@YAXXZ 100174d0 f   splash.obj
 0001:00016500       ??__EpServices@@YAXXZ      10017500 f   services_spl.obj
 ...

Currently the trace function writes the trace file at a defined time. This should be changed so this can be controlled from the application code. The trace file has the following format:

Part from a trace file
splmi.dll, Baseaddress: 0x03aa0000
1, 0x03ab74d0, 1
2, 0x03ab7500, 1
3, 0x03ab7530, 1
4, 0x03aa6a20, 1
5, 0x03aa6d30, 1
6, 0x03aa6f60, 1
7, 0x03aa70e0, 1
8, 0x03aa7150, 2
9, 0x03aa3d20, 3
10, 0x03aa6150, 2
11, 0x03aa6650, 2
12, 0x03aa60e0, 2
13, 0x03aa7230, 1
14, 0x03aa4540, 1
15, 0x03aa1000, 1
16, 0x03aa2180, 1
17, 0x03aa1d80, 6
18, 0x03aa2080, 12
19, 0x03aa20f0, 12
20, 0x03aa2b50, 11
21, 0x03aa4790, 5
22, 0x03aa47b0, 5
...

The first column is just a sequence number for the first access, the second column is the virtual address of the function and the third column the number of accesses to the function.

Combine informtion from the trace and map file to create the order file

Now we have all information necessary to create an order file for an optimized linker run. The symbol can be retrieved from the virtual address written to the trace file and the content of the map file. Let's see how this can be done using the first entry from the snippet of trace file further above.

splmi.dll, Baseaddress: 0x03ab0000
1, 0x03ac74d0, 1
 
Calculating the RVA (relative virtual address):
RVA = 0x03ac74d0 (virtual address) - 0x03ab0000 (virtual module base address)
RVA = 0x000174d0
 
Look up into the map file:
--------------------------
The base address for the map symbols is: 0x10000000
 
Address       Publics by Value                                          Rva+Base     Lib:Object
0001:000164d0 ??__E?_aMutex@SplashScreen@desktop@@0VMutex@osl@@A@@YAXXZ 100174d0 f   splash.obj
 
RVA = 0x100174d0 (Rva+Base) - 0x10000000 (Base)
RVA = 0x000174d0
 
So we have a hit and the first function (symbol) that is called in the splmi.dll:
decorated name                                       : ??__E?_aMutex@SplashScreen@desktop@@0VMutex@osl@@A@@YAXXZ 
undecorated name (according to VisualStudio Debugger): dynamic initializer for 'desktop::SplashScreen::_aMutex'
 
Unfortunately this symbol/function is static as it's located in the static part of the map. Therefore we cannot use it for the order file as the linker ignores static symbols.

Problems

There are some problems with the ORDER file and the linker.

Documentation caution.png The linker crashes reproducable if very long symbols are inside the ORDER file. A symbol with 1670 character length works, a symbol with 3345 chars results in a crash. It looks like that the linker works with a predefined buffer size for the symbols in the ORDER file. It must be verified if linker can order a symbol if it uses less characters.
Documentation caution.png The compiler uses a random number for every type that is declared in a anonymous or counted namespace. This number is newly created for every new compile process. Therefore these symbols cannot be used in ORDER files as the trace code needs an instrumented build which has its own random numbers.


Results

First tests on Windows with reordered symbols (all symbols which are needed during start up are sorted at the start of the library) shows that up to 40% less page faults could be reached (measured with Process Monitor). Look at the following table which provides numbers for some libraries. These are very early test results with prototype code, hopefully it can be further optimized. There are also some strange results which must be analyzed in more detail.

Test machine

  • Windows XP Professional SP3
  • Athlon XP 2800+ (2083Mhz)
  • 768MB RAM
  • Samsung 120GB 3.5" 2MB IDE 7200 Hard Disk Drive
  • Prefetch disabled


Module Page Faults (non-optimized) Page Faults (optimized) Time for all Read Operations (non-optimized) Time for all Read Operations (optimized) Improvement (Page Faults/Time)
swmi.dll 210 125 1378ms 866ms 37% / 37%
sfxmi.dll 110 86 912ms 659ms 22% / 28%
vclmi.dll 100 87 645ms 525ms 13% / 18%
fwkmi.dll 72 68 422ms 544ms 6% / -29% (*)
tlmi.dll 26 26 158ms 195ms 0% / -23% (*)
svxmi.dll 247 181 1208ms 855ms 27% / 30%
svtmi.dll 94 75 559ms 424ms 21% / 24%
svlmi.dll 32 31 189ms 239ms 3% / -26% (*)

(*) There are some indications why some of the optimized libraries are loaded slower. Due to the limited Microsoft linker capabilities to order symbols it's not possible to group all symbols together which are needed during start up. In the end the sum of distances between all needed pages is in the end higher than for the non-optimized version! Even reducing the amount of page faults cannot resolve this problem. The libraries which see a performance hit only see a small reduction of page faults. See the following table which provides some Performance Monitor data regarding the fwkmi.dll library.

Overall the load time for the first test set (13 optimized libraries) could be reduced by ~20%.

Example for the negative effect of limited symbol order optimization (fwkmi.dll)

Non-optimized library Seq. of read operation Duration of the read operation in sec. Offset into the library Number of bytes read Distance to the read operation before Optimized library Duration of the read operation in sec. Offset into the library Number of bytes read Distance to the read operation before
1 0,01011690 0 4096 0 0,01004480 0 4096 0
2 0,00934770 1310720 16384 1310720 0,00920080 1310720 16384 1310720
3 0,00697820 1758720 1536 448000 0,00698870 1758720 1536 448000
4 0,00024110 1654784 16384 103936 0,00021060 1654784 16384 103936
5 0,00020020 1228800 16384 425984 0,00019160 1228800 16384 425984
6 0,00023190 1671168 16384 442368 0,00022870 1671168 16384 442368
7 0,00117200 1708032 16384 36864 0,00116130 1708032 16384 36864
8 0,00025590 1691648 16384 16384 0,00019720 1691648 16384 16384
9 0,00016690 1687552 4096 4096 0,00015960 1687552 4096 4096
10 0,00022470 1724416 14336 36864 0,00021890 1724416 14336 36864
11 0,00024120 1742848 15872 18432 0,00024040 1742848 15872 18432
12 0,00466450 971776 32768 771072 0,00467340 971776 32768 771072
13 0,00032770 939008 32768 32768 0,00032300 939008 32768 32768
14 0,00242150 1197056 31744 258048 0,00241900 1197056 31744 258048
15 0,00016270 1738752 16384 541696 0,00015600 1738752 4096 541696
16 0,00024500 1245184 16384 493568 0,00022670 1245184 16384 493568
17 0,00023900 1261568 16384 16384 0,00023310 1261568 16384 16384
18 0,00024110 1277952 16384 16384 0,00022520 1277952 16384 16384
19 0,00037880 1294336 16384 16384 0,00040200 1294336 16384 16384
20 0,00498520 693248 32768 601088 0,00390660 480256 32768 814080
21 0,00033700 103424 32768 589824 0,00063340 447488 32768 32768
22 0,00380090 906240 32768 802816 0,02105090 771072 32768 323584
23 0,02214140 152576 32768 753664 0,00071310 570368 32768 200704
24 0,00033420 62464 32768 90112 0,00425740 414720 32768 155648
25 0,00033180 234496 32768 172032 0,00584710 29696 32768 385024
26 0,00034920 29696 32768 204800 0,00486590 824320 32768 794624
27 0,00031510 644096 32768 614400 0,01030090 656384 32768 167936
28 0,00026840 185334 32768 458762 0,00027560 381952 32768 274432
29 0,03073340 308224 32768 122890 0,00840460 738304 32768 356352
30 0,00063740 275456 32768 32768 0,00947990 1384448 16384 646144
... ... ... ... ... ... ... ... ...
60 0,01025040 533504 12288 1072128 0,00590920 259072 32768 1223680
61 0,00523330 1037312 32768 503808 0,00020940 1622016 16384 1362944
62 0,00657450 1449984 16384 412672 0,00041330 1147904 16384 474112
63 0,00022770 1523712 16384 73728 0,00071820 1585152 16384 437248
64 0,01006730 1335296 16384 188416 0,00584720 291840 32768 1293312
65 0,00023860 1351680 16384 16384 0,00833610 324608 24576 32768
66 0,00499920 1638400 16384 286720
67 0,00021360 1482752 16384 155648
68 0,00021900 1622016 16384 139264
69 0,01140220 1147904 16384 474112
70 0,00022650 1585152 16384 437248
Sum 0,25621180 1587200 21660692 0,26112620 1529856 28928000

Although the optimized version needs 5 less read operations and loads 4% less data into memory the read operations needed about 1% more time. There are other runs on slower test machines where the distance is greater (up to 30%)! The sum of distances between a previous and following read operation is 33% higher for the optimized library! That means we are not able to group the symbols together as necessary with the limited Microsoft linker capabilities.

Cold start up performance of OpenOffice.org 3.1 (DEV300m40)

I made some start up tests with a standard, a optimized version (just have 13 optimized/reordered symbols libraries) and one without rebased libraries (means every library has the same virtual base address so Windows needs to make relocations). Yuan Cheng from IBM reported that non-rebased libraries can boost cold start up performance significantly.

Test machine:

  • Windows Vista Ultimate 32-Bit
  • Opteron 175 (Dual core) 2,2Ghz
  • 4 GB RAM
  • Deskstar 7K250 160GB 8MB Cache
  • (Super Fetch and Prefetch disabled)


Optimization method Test run 1 Test run 2 Test run 3 Mean time
DEV300m40 (standard) 16,05s 16,38s 16,24s 16,23s (100%)
DEV300m40 (reordered symbols) 15,10s 15,05s 15,00s 15,05s (-7,3%)
DEV300m40 (not rebased/reordered) 12,89s 12,58s 12,74s 12,73s (-21,6%)

It looks like that reordering cannot provide the same performance boost that you can reach if one don't rebase the libraries. The positive effect of not rebasing is, that most libraries are loaded in one piece synchronously into memory. Therefore a disk is able to read the file sequentially. This is not possible with optimizing the order of symbols. The Microsoft linker is very limited to influence the order of symbols. Static symbols cannot be moved, anonymous namespaces which are often use in OpenOffice.org makes it impossible to move these symbols, too. Symbols with a certain length lead to linker crashes. All these problems lead to limited optimizations. Which in result cannot match the "brute force" solution to not rebase the libraries for better cold start behavior.

Non-rebased OpenOffice.org

There are some drawbacks to not rebase libraries. It must be clarified how severe these drawbacks are:

Drawbacks

  • Relocating needs some CPU power.
  • During start up the application needs more memory. All pages that have code/data which need relocations will be read into memory.
  • All pages which need fix ups must be reloaded from the swap file and not from the image file. That means that non-rebased libraries decrease the amount of virtual memory. See this web page for more information (although fairly old it's true for newer OS)
  • Contiguous address space could be decreased. See the following web page for more information: Rebasing DLLs on Windows
  • Symbol resolving for stack traces could be a problem. You need to know where the library was loaded when a crash occurred.

Findings

Performance and memory data

Some performance (warm start up) and memory values for DEV300m40 for both standard and non-rebased versions.

Attributes DEV300m40 (standard) DEV300m40 (non-rebased) Difference (reference is standard)
Virtual Size 283.040 KB 283.040 KB 0%
Working Set (WS) 55.152 KB 86.392 KB +57%
WS Private 18.048 KB 57.204 KB +317%
WS Shareable 37.104 KB 29.204 KB -21%
WS Shared 7.556 KB 7.476 KB -1%
Total CPU Time 1,653s 1,747s +6% (average values)
Increase of page file usage 27 MB 61 MB +226%
Library sharing

Not rebasing libraries has an impact on memory usage. Pages with relocated code/data cannot be shared between processes when they don't use the same virtual address for the library. The following tests want to find out how severe this problem is. One would think that starting the same executable (in this case swriter.exe -env:UserInstallation=<file URL to the user folder>) several times should lead to a high amount of library sharing (at least for code and read-only data sections).

The Vmmap application from Microsoft (http://technet.microsoft.com/en-us/sysinternals/dd535533.aspx) can help us to see how the libraries, heap and stack are spread in the process address space. The following table is a small part from the Vmmap output for four process started one after the other.

Virtual Address Process 1 Process 2 Process 3 Process 4
0x00070000 uwinapi.dll uwinapi.dll uwinapi.dll uwinapi.dll
0x000A0000 Shareable Shareable sofficeapp.dll sofficeapp.dll
0x00130000 Heap Default(Private) salhelper3MSC.dll
0x001C0000 sofficeapi.dll sofficeapp.dll
0x00220000 comphelp4MSC.dll comphelp4MSC.dll
0x00230000 comphelp4MSC.dll
0x00240000 comphelp4MSC.dll
0x00310000 cppuhelper3MSC.dll cppuhelper3MSC.dll
0x00320000 cppuhelper3MSC.dll
0x00330000 cppuhelper3MSC.dll
0x00390000 salhelper3MSC.dll salhelper3MSC.dll salhelper3MSC.dll
0x003B0000 cppu3.dll cppu3.dll cppu3.dll cppu3.dll
0x00400000 soffice.bin soffice.bin soffice.bin soffice.bin
0x01BB0000 stlport_vc7145.dll stlport_vc7145.dll stlport_vc7145.dll stlport_vc7145.dll
0x01C50000 ucbhelper4MSC.dll ucbhelper4MSC.dll ucbhelper4MSC.dll ucbhelper4MSC.dll
0x01CC0000 vos3MSC.dll vos3MSC.dll vos3MSC.dll vos3MSC.dll
0x10000000 sal3.dll sal3.dll sal3.dll sal3.dll

Unfortunately Windows is not able to share the text part of a library between processes even if the text part is loaded at the same virtual address. If we look deeper into the Vmmap output you can see the following details for the vclmi.dll.

OpenOffice.org non-rebased vclmi.dll

Virtual Address Type Size Committed Total WS Private WS Shareable WS Protection Details
0x02330000 Image 3.016K 3.016K 2.624K 2.108K 516K Execute/Copy on Write C:\Program Files\OpenOffice.org 3\Basis\program\vclmi.dll
0x02330000 Image 4K 4K 4K 4K Read Header
0x02331000 Image 1.792K 1.792K 1.752K 1.752K Execute/Read .text
0x024F1000 Image 764K 764K 716K 316K 400K Read .rdata
0x025B0000 Image 32K 32K 32K 32K Read/Write .data
0x025B8000 Image 272K 272K Copy on write .data
0x025FC000 Image 8K 8K 8K 8K Read/Write .data
0x025FE000 Image 144K 144K 112K 112K Read .rsrc

The section .text is part of the Private WS and therefore not shared between processes.

OpenOffice.org with rebased vclmi.dll

Virtual Address Type Size Committed Total WS Private WS Shareable WS Protection Details
0x56F60000 Image 3.016K 3.016K 1.672K 24K 1.648K Execute/Copy on Write C:\Program Files\OpenOffice.org 3\Basis\program\vclmi.dll
0x56F60000 Image 4K 4K 4K 4K Read Header
0x56F61000 Image 1.792K 1.792K 1.128K 1.128K Execute/Read .text
0x57121000 Image 764K 764K 504K 8K 496K Read .rdata
0x571E0000 Image 4K 4K 4K 4K Read/Write .data
0x571E1000 Image 12K 12K 4K 4K Copy on write .data
0x571E4000 Image 4K 4K 4K 4K Read/Write .data
0x571E5000 Image 284K 284K 4K 4K Copy on write .data
0x5722C000 Image 8K 8K 8K 8K Read/Write .data
0x5722E000 Image 144K 144K 12K 12K Read .rsrc

Microsoft Linker switch /SWAPRUN

The Microsoft linker supports a switch which is called /SWAPRUN:[NET|CD]. This sets a flag within a library/executable to inform the loader to read the whole image and write it into the swap file for later use. The possible values NET and CD give hints when Windows should activate this copy mechanism (NET=network drive, CD=Removable drive). This should help applications to run normally (while the system use on-demand paging) even when the network is down or the CD has been removed. We want to see if this switch could be interesting for our goal to improve library loading on cold start up. Unfortunately Windows clearly separates between normal and network/removable drives. Means the positive effect of synchronous and sequential library loading can only be seen for these drives.

Microsoft Linker switch /DYNAMICBASE

Starting with Visual Studio 2005 SP1 the Microsoft linker supports a new flag called /DYNAMICBASE. This flag controls a new security feature introduced for Windows Vista that is called ASLR (Address Space Layout Randomization). You find more information about ASLR here http://technet.microsoft.com/en-us/magazine/cc162458.aspx. Libraries which include this flag cannot be rebased to a certain virtual load address.

Linux

On Linux and Solaris, the soffice wrapper script spawns a helper tool pagein to pre-load the relevant libraries needed during start-up of soffice.bin. This greatly reduces the number of I/O-incurring page faults during start-up of soffice.bin. Currently (i.e., without symbol reordering), it is faster to let pagein pre-load everything than to let the OS demand-load what is actually needed. It would be interesting to see what the numbers would be with symbol reordering and without pagein.

MacOS X

The following web page from Apple describes what must be done to reorder code/data of a library to improve locality.

The subject has been proposed to the students in the Education Project Effort. Direct link

Solaris

OpenOffice.org uses the Sun Studio C++ compiler suite for building on both Sparc and x86 CPU systems. The following web page describes what can be done to optimize the code layout of libraries with the Sun Studio C++ compiler suite.

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