 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
.NET Forum / Languages / Managed C++ / January 2005Managed function vs unmanaged function
Hello everybody! I have a question. Anybody knows why managed function calls faster in MC++ rather than unmanaged function (defined with #pragma umanaged)? The differences is about 4 times slower. Thanks for your answers! Z-Mechanic. Could you send us some code with compiler switches you used so that we can do performance comparisons ? For eg, is the function you are trying to call virtual ? Is it called from a managed callsite ? Did you compile it pure? Thanks, Kapil > Hello everybody! > [quoted text clipped - 4 lines] > Thanks for your answers! > Z-Mechanic. Hi! I have a math library that makes 3D matrices (4x4) multiplication. After compillation it placing in same assembly. When I compile that source with #pragma unmanaged it works 2 times faster rather tham managed. It's fine. But... Simple test. Source code of test files listed below. Simply call TestCPP::Class1::Test(0); ---- Begin of TestCPP.h ---- // TestCPP.h #pragma once using namespace System; int vvv(int i); int vvv1(int i); int vvv2(int i); int vvv3(int i); int vvv4(int i); int vvv5(int i); namespace TestCPP { public __gc class Class1 { public: static void Test(int v) { int m = 0; for (int j = 0; j < 100; j++) for (int i = 0; i < 1000000; i++) { m = vvv( i ); // m = vvv1( i ); // m = vvv2( m ); // m = vvv3( m ); // m = vvv4( m ); // m = vvv5( m ); } m++; } }; } ---- End of TestCPP.h ---- ---- Begin of TestCPP.cpp ---- // This is the main DLL file. #include "stdafx.h" #include "TestCPP.h" #pragma unmanaged int vvv(int i) { i = vvv1( i ); i = vvv2( i ); i = vvv3( i ); i = vvv4( i ); i = vvv5( i ); return i; } int vvv1(int i) { i++; return i; } int vvv2(int i) { i++; return i; } int vvv3(int i) { i++; return i; } int vvv4(int i) { i++; return i; } int vvv5(int i) { i++; return i; } #pragma managed ---- End of TestCPP.cpp ---- ------------------------------------------------------------------------------------------------ It makes the same. But when you uncomment calls vvv1, vvv2, vvv3, vvv4, vvv5 and comment vvv you will get execution much longer that present now. It can be down to managed / unmanaged transitions, depend on what's going on inside the function, and lots of other factors. If you could post the function along with its calling context, someone will be able to give you a definitive explanation. We didn't actually find a significant performance hit when we eradicated all the "#pragma unmanaged" directives from our maths code, and we found that performance could be greatly affected by unnecessary managed/unmanaged transitions. Unless you've got a really good reason to use #pragma unmanaged, and unless that chunk of code is fairly large and doesn't call back into managed code, you might be better leaving it all as managed code. Steve > Hello everybody! > [quoted text clipped - 4 lines] > Thanks for your answers! > Z-Mechanic. Hi! I have a math library that makes 3D matrices (4x4) multiplication. After compillation it placing in same assembly. When I compile that source with #pragma unmanaged it works 2 times faster rather tham managed. It's fine. But... Simple test. Source code of test files listed below. Simply call TestCPP::Class1::Test(0); ---- Begin of TestCPP.h ---- // TestCPP.h #pragma once using namespace System; int vvv(int i); int vvv1(int i); int vvv2(int i); int vvv3(int i); int vvv4(int i); int vvv5(int i); namespace TestCPP { public __gc class Class1 { public: static void Test(int v) { int m = 0; for (int j = 0; j < 100; j++) for (int i = 0; i < 1000000; i++) { m = vvv( i ); // m = vvv1( i ); // m = vvv2( m ); // m = vvv3( m ); // m = vvv4( m ); // m = vvv5( m ); } m++; } }; } ---- End of TestCPP.h ---- ---- Begin of TestCPP.cpp ---- // This is the main DLL file. #include "stdafx.h" #include "TestCPP.h" #pragma unmanaged int vvv(int i) { i = vvv1( i ); i = vvv2( i ); i = vvv3( i ); i = vvv4( i ); i = vvv5( i ); return i; } int vvv1(int i) { i++; return i; } int vvv2(int i) { i++; return i; } int vvv3(int i) { i++; return i; } int vvv4(int i) { i++; return i; } int vvv5(int i) { i++; return i; } #pragma managed ---- End of TestCPP.cpp ---- ------------------------------------------------------------------------------------------------ It makes the same. But when you uncomment calls vvv1, vvv2, vvv3, vvv4, vvv5 and comment vvv you will get execution much longer that present now. This is related to exactly what I said; in your managed call, you go from calling one unmanaged function to calling 5. When they're wrapped into a single unmanaged function in the DLL, there's less managed -> unmanaged transitions, and less DLL overheads. There was a nother thread on here a few days ago about all this, and there's lots of info on the net. I can't see much advantage making this unmanaged, to be honest - I doubt you'll see a big performance increase. Steve > Hi! > [quoted text clipped - 102 lines] > vvv5 > and comment vvv you will get execution much longer that present now. Hi! Greate thanks for explanations! It was a test only to check perfomance on procedure calling. As I said before I got a great increase of perfomance on a complex math functions when I put my code to unmanaged. Hi, Yes, typically with complex instructions you will find performance increases. It's just important to ensure that you're not constantly transitioning between managed and unmanaged code, or you'll lose the benefits. I'm sorry I can't find the explanation of all this; if you Google for something like "Unmanaged managed code transition" you'll probably get some info. Steve > Hi! > [quoted text clipped - 4 lines] > when > I put my code to unmanaged. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
|
Reply to this Message
|
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2008 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.