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Re: profiler and/or debugger, loops vs vectorization

From: David Bateman
Subject: Re: profiler and/or debugger, loops vs vectorization
Date: Sat, 01 Jul 2006 18:19:42 +0200
User-agent: Mozilla Thunderbird 1.0.6-7.6.20060mdk (X11/20050322)

David Grohmann wrote:
> So I have some code that runs in matlab (on a P3 500 mhz 512 MB ram 
> windows box) about 133 times faster (33 minutes to complete something 
> instead of 15 seconds)  than it does in octave( on a 4 processor 3.6 ghz 
> xeon machine with an ungodly amount of ram linux box). my guess is that 
> it is the use of loops and not vectorization.
> Is such a large performance hit likely caused by loops vs vectorization 
> or might there be another explanation besides that?
> I've searched online and haven't found anything to profile m files with, 
> other than in matlab. I have profiled it in matlab and sure enough it 
> does run the lines in the loops many (hundreds of thousands of times) 
> times but only one of the loops actually takes up a lot of run time. 
> This would probably be a good candidate for vectorizing. I suspect.
> So is there anything out there for profiling or stepping through code in 
> an m file in octave?
> I know I haven't posted the offending code, that is because I currently 
> don't have the authorization to do that. So my general question is how 
> do people profile their code and what not. I'm not asking you to fix my 
> code for me.
> Thank you for any help you provide,

My guess is that you are running a cygwin binary version of octave.
There is a major bug in the setjmp/longjmp exception handler of g++ for
versions later than 3.2 that causes major pain to octave. As far as I
know this bug in cygwin as not yet been addressed. The result is
sssllloooowwww code..


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