CODEWITHSUNDEEP
c++macosprofilingmpicode-analysis
Chris
Chris

Reputation: 2060

C++ Code profiling/analysis for Mac and MPI

I am looking for a code analysis/profiling tool for C++ on MacOS. I know that there have been posts about this thread, but my application in which I need is very specific, so maybe one can give me a little more specific advice.

So here is my problem: I am writing a scientific code (master's project) in C++, so it's a pure console application, no interactivity given. The code is supposed to run on massively parallel computers, thus I use MPI. However, right now I am not yet optimizing for scalability, but only for singlecore performance. Since I do not want to rewrite the whole programm as a serial one, I just use MPI with 1 thread. It works fine, but the optimizer obviously needs to be able to deal with this.

What do I want to analyze? Well, the code is not very complex in a sense that it has a very simple structure and thus all I need would be a list of how long the program spends in certain functions, so that I know where it loses most time and I can measure the speedup of my optimizations.

Thanks for all ideas

Upvotes: 5

Views: 3511

Answers (4)

Mike Dunlavey
Mike Dunlavey

Reputation: 40659

Don't look for "slow functions" and don't look to measure the time used by different pieces. Those concepts are so indirect as to be almost useless for telling you what to optimize.

Instead, take some stroboscopic X-rays, on wall-clock time, of what the entire program is doing, and study each one to see why the program is spending that instant of time. The reason this works better is it's not looking with function-colored glasses. It's looking with purpose-colored glasses, and you can tell if the program needs to be doing what it's doing. It's very accurate about locating big problems. It is not accurate about measuring them, nor does it need to be.

What happens when you just do measuring is this: You get a bunch of numbers on a bunch of routines. You look at them and say "what does it mean?". If it doesn't tell you what you should fix, you pat yourself on the back and say the program must be optimal. In fact, there probably is something you could fix, but you couldn't figure it out from the profiler. What's more, if you do find it and fix it, it can expose other things you can fix for even greater speedup.

That's what random pausing is about.

Upvotes: 1

Vladimir F Героям слава
Vladimir F Героям слава

Reputation: 60008

I can recommed http://www.scalasca.org/ . You can use it also for the parallel performance afterwards.

Upvotes: 1

nielsbot
nielsbot

Reputation: 16022

You should use Instruments.app which includes a CPU sampler and thread activity viewer... among other things. (Choose "Product > Profile..." in Xcode)

If you want something more fine-grained, you could instrument your code. Coincidentally, I wrote a set of profiling macros just for such an occasion :)

https://github.com/nielsbot/Profiler

This will show a nice nested print out of time spent in instrumented routines. (instructions on that page)

Upvotes: 3

gregory561
gregory561

Reputation: 15046

Did you try kcachgrind: http://kcachegrind.sourceforge.net/html/Home.html with valgrind ?

Upvotes: 1

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