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Speed Optimization of C++ console application



  • Hi,
    I am relatively new to programming and am a complete newbie to QT. I have been creating a C++ console application in visual studio 2017 that is basically the matrix calculation engine of a new app I want to develop. In visual studio, I optimized this program using the 02 speed optimization setting and the console app performs the calculations very quickly.

    Now that I have the calculation engine complete, I want to create a GUI for the program. That is when I turned to QT. To "get my feet wet" in QT I created a new simple C++ console app and brought in all of my header and source files. I inserted QMAKE_CXXFLAGS_RELEASE -= -O2 and QMAKE_CXXFLAGS_DEBUG -= -O2 into the .pro file and ran QMake. However, when I run the app itself it is approximately 10x slower than the same exact app compiled and run from VS.

    In VS2017 the total calculation time is 1.2 seconds
    In QT4.10.2 the same exact calculation time is 13.1 seconds

    Can anyone give me some pointers as to what I am missing?

    Thanks in advance....



  • @dooley Hi, you build it with mingw or MSVC?
    Also, could you please post your .pro file please?



  • @dooley said in Speed Optimization of C++ console application:

    In QT4.10.2 the same exact calculation time is 13.1 seconds

    QtCreator is just an IDE, it depends on which Qt Kit (MSVC2017, MinGW, etc..) you have used for your project and in what configuration (release, debug or profile) you have build the project.


  • Lifetime Qt Champion

    @dooley said in Speed Optimization of C++ console application:

    QMAKE_CXXFLAGS_RELEASE -= -O2

    Shouldn't that be QMAKE_CXXFLAGS_RELEASE += -O2 if you want to optimize for speed?

    Regards



  • @aha_1980
    Good catch! Now if people put

    `code`
    

    tags into their questions like you have we would be able to spot these things :)



  • @artwaw I am building with MSVC 2017 64 bit .

    I must be doing something wrong because I am getting the same calculation speed if I include
    the CXXFlags in hte pro file or not. In visual studio there was dramatic 20x speed increase in the app by just adding 02 optimization.

    I have pasted my pro file below

    TEMPLATE = app
    CONFIG += console c++11
    CONFIG -= app_bundle
    CONFIG -= qt
    
    
    QMAKE_CXXFLAGS_RELEASE -= -O2
    
    
    SOURCES += \
            CVSReader.cpp \
            ComponentManagement.cpp \
            MatrixUtilities.cpp \
            Nodes.cpp \
            Pipes.cpp \
            Tanks.cpp \
            VectorUtilities.cpp \
            main.cpp
    
    HEADERS += \
        CVSReader.h \
        ComponentManagement.h \
        Globals.h \
        MatrixUtilities.h \
        Nodes.h \
        Pipes.h \
        Tanks.h \
        VectorUtilities.h \
        resource.h
    
    
    INCLUDEPATH += $$PWD/../C++Libraries/Eigin3.3.7
    DEPENDPATH += $$PWD/../C++Libraries/Eigin3.3.7
    


  • @dooley said in Speed Optimization of C++ console application:

    QMAKE_CXXFLAGS_RELEASE -= -O2

    Have you read @aha_1980 's answer above?



  • @JonB Yes I saw it. I did try changing it to QMAKE_CXXFLAGS_RELEASE += -02 as suggested and saw no improvement. I will change it back if that is the correct way to insert it... like I said I am new to QT and saw the -= format in another post and was tying it.

    Thanks for the response... do you have any other thoughts as to why I don't see an increase in speed?

    Sorry it took so long to respond to you but since I am a new user I have to wait 600 seconds between posts.


  • Lifetime Qt Champion

    @dooley

    So are you actually building a release version?

    Please show your compiler output so we see the flags passed to the compiler.

    Sorry it took so long to respond to you but since I am a new user I have to wait 600 seconds between posts.

    No longer, I gave you an upvote :)

    Regards



  • @aha_1980 Here is the compiler output...

    15:08:01: Running steps for project SF_1...
    15:08:01: Configuration unchanged, skipping qmake step.
    15:08:01: Starting: "C:\Qt1\Tools\QtCreator\bin\jom.exe" 
    	C:\Qt1\Tools\QtCreator\bin\jom.exe -f Makefile.Release
    15:08:01: The process "C:\Qt1\Tools\QtCreator\bin\jom.exe" exited normally.
    15:08:01: Elapsed time: 00:00.
    


  • @aha_1980 This is probably more usefull :)

    15:18:51: Running steps for project SF_1...
    15:18:51: Starting: "C:\Qt1\Tools\QtCreator\bin\jom.exe" clean
    	C:\Qt1\Tools\QtCreator\bin\jom.exe -f Makefile.Release clean
    	del release\CVSReader.obj release\ComponentManagement.obj release\MatrixUtilities.obj release\Nodes.obj release\Pipes.obj release\Tanks.obj release\VectorUtilities.obj release\main.obj
    	C:\Qt1\Tools\QtCreator\bin\jom.exe -f Makefile.Debug clean
    	del debug\CVSReader.obj debug\ComponentManagement.obj debug\MatrixUtilities.obj debug\Nodes.obj debug\Pipes.obj debug\Tanks.obj debug\VectorUtilities.obj debug\main.obj
    	del debug\SF_1.vc.pdb debug\SF_1.ilk debug\SF_1.idb
    Could Not Find C:\Users\heath\Documents\build-SF_1-Desktop_x86_windows_msvc2017_pe_64bit-Release\debug\CVSReader.obj
    Could Not Find C:\Users\heath\Documents\build-SF_1-Desktop_x86_windows_msvc2017_pe_64bit-Release\debug\SF_1.vc.pdb
    15:18:52: The process "C:\Qt1\Tools\QtCreator\bin\jom.exe" exited normally.
    15:18:52: Starting: "C:\Qt1\5.13.1\msvc2017_64\bin\qmake.exe" C:\Users\heath\Documents\SF_1\SF_1.pro -spec win32-msvc "CONFIG+=qtquickcompiler"
    15:18:52: The process "C:\Qt1\5.13.1\msvc2017_64\bin\qmake.exe" exited normally.
    15:18:52: Starting: "C:\Qt1\Tools\QtCreator\bin\jom.exe" -f C:/Users/heath/Documents/build-SF_1-Desktop_x86_windows_msvc2017_pe_64bit-Release/Makefile qmake_all
    
    jom 1.1.3 - empower your cores
    
    15:18:52: The process "C:\Qt1\Tools\QtCreator\bin\jom.exe" exited normally.
    15:18:52: Starting: "C:\Qt1\Tools\QtCreator\bin\jom.exe" 
    	C:\Qt1\Tools\QtCreator\bin\jom.exe -f Makefile.Release
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\CVSReader.obj.4364.15.jom
    CVSReader.cpp
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\VectorUtilities.obj.4364.78.jom
    VectorUtilities.cpp
    ..\SF_1\VectorUtilities.cpp(43): warning C4244: '=': conversion from '__int64' to 'int', possible loss of data
    ..\SF_1\VectorUtilities.cpp(55): warning C4244: '=': conversion from '__int64' to 'int', possible loss of data
    ..\SF_1\VectorUtilities.cpp(60): warning C4244: '=': conversion from '__int64' to 'int', possible loss of data
    ..\SF_1\VectorUtilities.cpp(70): warning C4189: 'tmp': local variable is initialized but not referenced
    ..\SF_1\VectorUtilities.cpp(96): warning C4189: 'tmp': local variable is initialized but not referenced
    ..\SF_1\CVSReader.cpp(16): warning C4189: 'numLines': local variable is initialized but not referenced
    ..\SF_1\CVSReader.cpp(14): warning C4189: 'newLine': local variable is initialized but not referenced
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\Nodes.obj.4364.47.jom
    Nodes.cpp
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\ComponentManagement.obj.4364.15.jom
    ComponentManagement.cpp
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\MatrixUtilities.obj.4364.31.jom
    MatrixUtilities.cpp
    ..\SF_1\MatrixUtilities.cpp(367): warning C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data
    ..\SF_1\MatrixUtilities.cpp(437): warning C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data
    ..\SF_1\MatrixUtilities.cpp(385): warning C4189: 'tFI_T': local variable is initialized but not referenced
    ..\SF_1\MatrixUtilities.cpp(456): warning C4189: 'Ed': local variable is initialized but not referenced
    ..\SF_1\MatrixUtilities.cpp(829): warning C4267: 'initializing': conversion from 'size_t' to 'int', possible loss of data
    ..\SF_1\MatrixUtilities.cpp(829): warning C4189: 'loopcnt': local variable is initialized but not referenced
    ..\SF_1\MatrixUtilities.cpp(866): warning C4189: 'cheker': local variable is initialized but not referenced
    ..\SF_1\MatrixUtilities.cpp(860): warning C4189: 'end': local variable is initialized but not referenced
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\Pipes.obj.4364.47.jom
    Pipes.cpp
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\Tanks.obj.4364.62.jom
    Tanks.cpp
    	cl -c -nologo -Zc:wchar_t -FS -Zc:rvalueCast -Zc:inline -Zc:strictStrings -Zc:throwingNew -Zc:referenceBinding -Zc:__cplusplus -O2 -MD -O2 -W3 -w34100 -w34189 -w44996 -w44456 -w44457 -w44458 -wd4577 -wd4467 -EHsc -DUNICODE -D_UNICODE -DWIN32 -D_ENABLE_EXTENDED_ALIGNED_STORAGE -DWIN64 -DNDEBUG -I..\SF_1 -I. -I..\C++Libraries\Eigin3.3.7 -I..\..\..\..\Qt1\5.13.1\msvc2017_64\mkspecs\win32-msvc -Forelease\ @C:\Users\heath\AppData\Local\Temp\main.obj.4364.94.jom
    main.cpp
    ..\SF_1\main.cpp(33): warning C4101: 'my_documents': unreferenced local variable
    	link /NOLOGO /DYNAMICBASE /NXCOMPAT /INCREMENTAL:NO /SUBSYSTEM:CONSOLE "/MANIFESTDEPENDENCY:type='win32' name='Microsoft.Windows.Common-Controls' version='6.0.0.0' publicKeyToken='6595b64144ccf1df' language='*' processorArchitecture='*'" /MANIFEST:embed /OUT:release\SF_1.exe @C:\Users\heath\AppData\Local\Temp\SF_1.exe.4364.7000.jom
    15:18:59: The process "C:\Qt1\Tools\QtCreator\bin\jom.exe" exited normally.
    15:18:59: Elapsed time: 00:08.
    


  • @aha_1980 After having taken your and @aha_1980 direction on the annotation and rebuilding it appears to be working.

    Thanks to everyone for the help. I am a civil engineer putting together some simple apps for calculations I use regularly more for fun and the interest in programming than anything else, so I don't know a whole lot and can use as much help as I can get.



  • @dooley said in Speed Optimization of C++ console application:

    civil engineer

    Ah, a "target" maker. Welcome aboard!



  • When building in Release mode, the optimization flag -O2 should be set by default.

    If speed is an issue and using lots of loops you can also enable the logs for Auto-Vectorization:

    QMAKE_CXXFLAGS_RELEASE += -Qvec-report:2
    

    Then all vectorized and non-vectorized loops will be logged and you can see where loops can be imporved. For some loops it's neccessary to set

    QMAKE_CXXFLAGS_RELEASE += -fp:fast
    

    to be vectorized. But be careful with that!

    Another way to speed up the program is to set the -Qpar flag for Auto-Parallelization:

    QMAKE_CXXFLAGS_RELEASE += -Qpar
    

    Then, if possible, loops will be parallelized. There is also an log flag for that -QPar-report:2.

    Please note, only valid for MSVC compiler and CPU architure with SSE2, AVX, and AVX2.


  • Moderators

    @beecksche said in Speed Optimization of C++ console application:

    QMAKE_CXXFLAGS_RELEASE += -fp:fast
    

    Don't use this unless you really, really, really (and I can't emphasize that enough) know what you're doing (which is almost never). This can break promises made by the IEEE FP standard in regards to behavior and optimize out expressions that are not to be optimized. It can break proper rounding and error propagation, and floating point exceptions' diagnostics.



  • A code slowdown of a factor of 10 wouldn't be normal just with an optimization flag of -O0 vs -O2. Something else is going on here. The OP only states C++ in VS2017...No mention of CLR or native code generation in VS. Actually I'd expect the converse of the reported behaviour, where the native C++ QT runs faster if the VS C++ code is done as CLR and not native. If I had to WAG, I'd guess that the VS code is taking advantage of a .net library optimization that isn't present in native C++ QT. Without seeing the algorithms and the library links it's hard to know what exactly is going on. Heap managed memory could also play a large part in the time differences being reported.


  • Lifetime Qt Champion

    @Kent-Dorfman said in Speed Optimization of C++ console application:

    A code slowdown of a factor of 10 wouldn't be normal just with an optimization flag of -O0 vs -O2.

    Why not? Did you see the code? Maybe there are lots of asserts in there or other stuff... without code it's just wild guessing.


  • Moderators

    @Kent-Dorfman said in Speed Optimization of C++ console application:

    A code slowdown of a factor of 10 wouldn't be normal just with an optimization flag of -O0 vs -O2.

    Actually it can be pretty normal. I've at least two rather small codebases that exhibit such speedups between debug and release (i.e. -g -O0 vs -O2). There's nothing odd about it because debug mode represents what you wrote faithfully, which isn't at all true for release builds.

    Something else is going on here.

    Not necessarily. Depends on the type of code. If you have code with a lot of templates for example the debug build is going to put a call instruction on every function call and do the regular push, pop on the stack. When the optimizer runs almost, to all, of this gets stripped down and the code is inlined, to an extreme degree. So yes, 10 time speedup between debug and release is nothing to be suspicious about.



  • @dooley
    What the others are saying about optimization vs debug is probably correct, you can be surprised by how much difference it can make depending.

    However, if you are sure about your compiler flags etc. but are still stumped by speed behaviour, it may be time to compile/link for profiling your application. Both gcc & msvc have profiling (unless the free msvc does not, I don't know). This does take a bit of reading first time to set up and interpret output, but well worth it if you wish to investigate speed/performance over time in future.



  • @kshegunov I wrote absolutely nothing about "-g". I still maintain that simple -O0 vs -O2 is NOT going to divide performance by a factor of 10. I cannot begin to imagine how badly a person would have to design their algorithm to validate that level of performance hit. something other than compiler optimization is causing his hit...


  • Moderators

    @Kent-Dorfman said in Speed Optimization of C++ console application:

    @kshegunov I wrote absolutely nothing about "-g".

    Fair enough.

    I still maintain that simple -O0 vs -O2 is NOT going to divide performance by a factor of 10. I cannot begin to imagine how badly a person would have to design their algorithm to validate that level of performance hit.

    https://bitbucket.org/kshegunov/ans-utilities/src/master/hermite/

    Knock yourself out, if you so desire. I'm certainly not investing the time to see if -g makes a significant difference, which I strongly suspect it doesn't.


  • Lifetime Qt Champion

    @Kent-Dorfman said in Speed Optimization of C++ console application:

    @kshegunov I wrote absolutely nothing about "-g". I still maintain that simple -O0 vs -O2 is NOT going to divide performance by a factor of 10. I cannot begin to imagine how badly a person would have to design their algorithm to validate that level of performance hit. something other than compiler optimization is causing his hit...

    That strongly depends on the algorightm, I'd say.

    Just imagine, a non optimized build that does not fit in the cache, so the CPU has to re-load stuff from memory all the time vs. the optimized build that runs fluently.

    Factor 10 is probably not the normal case where you have to wait for I/O anyway, but for heavy computing it is easily possible.

    Regards



  • This is starting to sound like a coding challenge. Can you write an algorithm that is slow the compiler can optimize and make fast? Like turning lead to gold.


  • Moderators

    @fcarney said in Speed Optimization of C++ console application:

    Can you write an algorithm that is slow the compiler can optimize and make fast? Like turning lead to gold.

    As I wrote, any template nonsense you have (the deeper and nastier the better) fits into this category.



  • Eh, the OP kind of disappeared so I guess it isn't that important to him. I'm more interested in knowing whether the windoze version in this exercise was compiled to CLR bytecode, which he never answered, and which IMHO invalidates any real comparison.


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