In this article, we will explore the GNU profiling tool ‘gprof’. In this step, the gprof tool is run with the executable name and the above. What is gprof? Gprof is a profiling program which collects and arranges statistics on your programs. Write hate-mail to gnu (but don’t tell them I told you to). Table of Contents. 1. Introduction to Profiling · 2. Compiling a Program for Profiling · 3. Executing the Program · 4. gprof Command Summary · Output Options.
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Through profiling one can determine the parts in program code that are time consuming and need to be re-written. This helps make your program execution faster which is always desired. In very large projects, profiling can save your day by not only determining the parts in your program which are slower in execution than expected but also can help you find many hprof statistics through which many potential bugs can be spotted and sorted gu.
The last step above produces an analysis file which is in human readable form.
GPROF Tutorial – How to use Linux GNU GCC Profiling Tool
This file contains a couple of tables flat profile and call graph in addition to some other information. While flat profile gives an overview of the timing information of the functions like time consumption for the execution of a particular function, how many times it was called etc.
On the other hand, call graph focuses on each function like the functions through which a particular function was called, what all functions were called from within this particular function etc So this way one can get idea of the execution time spent in the sub-routines too.
Lets try and understand the three steps listed above through a practical example. Following test code will be used throughout the article:. In this first step, we need to make sure that the profiling is enabled when the compilation of the code is done. Generate extra code to write profile information suitable for the analysis program gprof. You must use this option when compiling the source files you want data about, and you must also use it when linking.
In the second step, the binary file produced as a result of step-1 above is executed so that profiling information can be generated. Note that while execution if the program changes the current working directory using chdir then gmon. Also, your program needs to have sufficient permissions for gmon. This produces an analysis file which contains all the desired profiling information.
Note that one can explicitly specify the output file like in example above or the information is produced on stdout. On a related note, you should also understand how to debug your C program using gdb. Lets have a look at this text file:.
The individual columns for the flat profile as well as call graph are very well explained in the output itself. There are various flags available to customize the output of the gprof tool. Some of them are discussed below:. If there are some static functions whose profiling information you do not require then this can be achieved using -a option:. As you would have already seen that gprof produces output with lot of verbose information so in case this information is not required then this can be achieved using the -b flag.
Note that I have used and will be using -b option so as to avoid extra information in analysis output. So we see that a flat profile containing information related to only function func1 is displayed. Also, if there is a requirement to print flat profile but excluding a particular function then this is also possible using -P flag by passing the function name to exclude along with it.
Now lets see the analysis output:. Also, if it is desired to suppress a specific function from call graph then this can be achieved by passing the desired function name along with the -Q option to the gprof tool.
Thank you very much, keep up the good work! I think it is better to make bigger time discrete in functions. In flat profile we expect that func1 works longer than func2. But because difference in loops is small, every time program executes we can get different sort results in flat profile. Sorry for bad English and thank you very much for this article.
I have been using gprof to isolate a performance issue in a large scale business application, but recent attempts to do this have stalled.
GPROF is not very good for what you need.
In a large application like yours, The flat profile is mainly about self time, which in a large program is usually irrelevant because the real problems are mid-stack. Well, I ran the proram again, and this time it produced the gmon. It produced the gmon. The only reason I came here is I was trying to remember why gmon. As usual in life, it is a matter of using the tool in the right way in addition to using the right tool and that involves having enough experience in order to interpret it you know, sort of like you don’t use a hammer to put a screw in a screw hole?
The same goes the other way around too. The man page, by the way, suggests this:. If you simply want to know which functions burn most of the cycles, it is stated concisely here. The call graph shows, for each function, which functions called it, which other functions it called, and how many times.
There is also an estimate of how much time was spent in the subroutines of each function. This can suggest places where you might try to eliminate function calls that use a lot of time. In other words, in the hands of an experienced programmer, it is a very valuable tool for exactly what you claim it isn’t good for.
Bugs listed are irrelevant as again, just because something has a problem does not mean it is useless or never useful in any way shape or form. Oh no, the world is NOT perfect and only a fool would think otherwise or think that only perfection is valuable. You raise a lot of valid points, but let me itemize my objections to gprof. That measuring time of functions is good enough as opposed to lines of code or even instructions. That recursion is a tricky confusing vnu it only is a problem when trying to construct an annotated call graph.
That accuracy of measurement is important as opposed to accuracy of identifying speedup opportunities. That samples need not be taken during IO or other blockage as opposed to sampling on wall-clock gpdof.
The human eye can recognize similarities between state samples stack and data that no summarizing backend of any profiler has any hope of exposing to the user.
Table of Contents
You can think the software is as fast as possible, when in fact it could be much faster. Well your points are also valid. I think point 10 is exactly what I was getting at: Indeed, it can always get faster and that is the con and pro of higher level languages; on the one hand, you can get more grof sooner but on the other hand the executable will be larger and the executable will not be as efficient or as fast.
The main thing I was getting at is gprof has its uses and to dismiss it entirely is not always helpful but then so would be dismissing your points — they are valid. Gproof that clears up any points from my end you did indeed clear up your points and I — besides being surprised you responded to me responding from your response from — appreciate it.
As a quick addendum: Also, I agree that recursion is not all that difficult. The reason ctrl-c prevents it from producing a gmon. So you need it to exit from program gprot normal termination.
My only comment here is that what we did get from the few profiling runs that ran to completion helped us identify exactly what the performance problems were.
I was much more concerned about why the profiling build of the app hung at the end, thereby preventing us from collecting the gmon,out files. Yes, I understand the limitations of most program analysis tools. Anyway, as for why it would hang, a gnh and a suggestion on figuring out where its having issues:. Okay, fprof that two questions three if you count the previous one as two: Anything else that is different should be kept in mind too including — just saying and not suggesting this is it — system load.
One final bprof is that it is almost always not a system library grof when you see something hanging or crashing in a system library e. Just mentioning that because I see that complaint a lot.
From attaching to the program during execution where you need to investigateyou then have an idea well, often where the problem is in which case you can get closer to solving the problem.
I have followups enabled so if you respond maybe I can help more.
What about cases where i need to know the time spent by each routine in nano seconds precession? Do you have any idea why? Notify me of followup comments via e-mail. Journey of a Data Packet in the Internet. All rights reserved Terms of Service.
GNU gprof – Table of Contents
It is easy to use,clearly and instructive. Dario August 13,8: Mike Dunlavey October 2,1: Rasna October 17, Could you please add details about how to get gmon. Antoha Bikineev October 30, Mark Richter February 13, This never happens when the non-profiling version is run. Why would the profiling version hang up at the end of program execution like that? Mike Dunlavey February 14,6: Alex February 21, Cody February gpror,7: The man page, by the way, suggests this: Mike Dunlavey February 28,7: Hi Cody, You raise a lot of valid points, but let me itemize my objections to gprof.
That program counter sampling is useful as opposed to stack sampling. That the call graph is important as opposed to the information in stack samples.