问题
EDIT 1
I do not exclude at all this might be caused by something very basic side effect of using the Profiler (some faulty setting in my "regular" project)
I wanted to improve Computing Time in my Application, so I decided to go through a thorough profiling analysis.
So I just launched a .Net Memory Allocation Profiling to analyze my App.
I was completely stunned to watch computing go x20 times faster !
Application consists of Reading Data from Binary Files with BackgroundWorkers, process them,
and store results into an MSSQL DB. Each round usually takes 20 seconds, and while profiling it barely takes 1 sec. I checked and made sure results are coherent in both cases.
A .Net experimented friend told me the profiler optimizes threading and "somehow" finds its way through thread Locks and Bottlenecks, but I just can't believe it.
So my questions are :
- WHAT EXACTLY HAPPENS, HOW, and WHY ?
- How to make my code behave like that natively ?
EDIT 2
I KNOW this sounds crazy and unbelievable. I myself am still very suspicious.But it's TRUE.
The SAME code runs really fast when run by the profiler.
I use the SAME test data, and watch the SAME computing output.
I am not able to give out a simple reproducing project, as it is a relatively big framework.
I am using the Visual Studio 2010 Profiler.
I'll be giving as much details as I can on the flow and definitely will post a clue as soon as I find it.
Regular RUN LOGS :
03/23/2011 18:04:34 | 180434.621 | SIMULATING SET [5]-[1]-[5 PC-1 0 [SET 1/48]
03/23/2011 18:05:01 | 180501.271 | PROCESSING TIME : 00:00:26.6515244
etc..
Profiler Run LOGS :
03/24/2011 11:38:15 | 113815.592 | SIMULATING SET [5]-[1]-[5 PC-1 0 [SET 1/48]
03/24/2011 11:38:17 | 113817.350 | PROCESSING TIME : 00:00:01.7581005
etc..
EDIT 3 : The Clue
Ok ok ok My BAD(I warned on such a possibility on edit 1, as this was too unbelievable. Sorry) @Watts suggested to check if I was in debug or release mode.
Which I had Already done. BUT @SnowBear pointed out that there are two different things : to run debug version of software and to run a software under debugger
I made sure that the active configuration was RELEASE in both Build And Execution is VS2010. However, as I was just going nuts I decided to launch the Application directly from the exe file in the bin/release. And voilà... processes were taking 1 second each.
Running the Profiler get you out of debug mode (whether you're in release or debug mode)
that's what put me into confusion.
Thanks to All Case Closed.
回答1:
Running with the debugger disables jit optimizations. If you run the exe normally jit optimizations will be enabled. Attaching a debugger to such a running application allows you to debug it with enabled optimizations.
Release-Build vs Debug-Build has two consequences:
- A conditional compiler symbol is (un)defined
- It enables/disables optimizations in the C# => IL compilation.
回答2:
Considering that the question is about code running faster under the profiler, and that the specific questions are "1. WHAT EXACTLY HAPPENS, HOW, and WHY ? and 2. How to make my code behave like that natively ?" the accepted answer is wrong, since it does not address the profiler at all, nor does it mention the specific cause of the 20x speed up.
What exactly happens is this:
In the "Debug" tab of your project properties the "Enable unmanaged code debugging" check box is checked; this option causes the debugger to be slow as molasses.
When you run the profiler, it is still the debug version of your program which you are profiling, so the "DEBUG" symbol is defined, and all the tracing, assertions, etc. are enabled, but the debugger is not involved, so the "Enable unmanaged code debugging" option is not applicable. (JIT optimizations are probably enabled while profiling, but that would not account for even a 2x performance boost, let alone a 20x boost.)
If you want to enjoy this 20x boost while debugging your code, (not only while profiling,) go to the "Debug" tab of your project properties and make sure that "Enable unmanaged code debugging" is unchecked.
P.S.
There is a question which is a few-month-older duplicate of this one: How Come when I sampling profile a program and it actually runs faster than not profiling?
回答3:
I've come across this many times... There is a very simple explanation for it. The profiler doesn't dispose objects, so the cost of object-disposal is not incurred while profiling.
Thus, if you want to improve performance to make it match the profiled performance, figure out where you're instantiating all these short-lived objects, and refactor the code.
I don't yet know of a really great way to immediately find the offending code, but I can help you narrow it down. If you profile your code, open the report, select "Functions" as your Current View, and then sort by Inclusive Samples, you will see the top methods... Your performance problem with object-instantiations is likely to be in one of those methods with the most Inclusive Samples.
来源：https://stackoverflow.com/questions/5417663/launching-vs-profiler-boosts-application-performance-x20