Re: [MLUG] Linux time command -- "kernel mode" and "user mode"

[Stephen Montgomery-Smith <EMAIL:PROTECTED>]

On Fri, 3 Nov 2006, Mike Miller wrote:

> On Fri, 3 Nov 2006, Stephen Montgomery-Smith wrote:
>
> > On Fri, 3 Nov 2006, Mike Miller wrote:
> >
> > > We have written a program in C++ and we have also written it with a 
> > > slightly different algorithm in Python.  We want to see how much slower 
> > > the Python program is than the C++ program.  We get these results:
> > >
> > > Python:
> > > ------
> > > real    10m43.357s
> > > user    9m51.050s
> > > sys     0m23.420s
> > >
> > > C++:
> > > ------
> > > real    8m16.668s
> > > user    5m38.360s
> > > sys     2m37.780s
>
> > This is my understanding.
> >
> > You want to add the user and kernel times together.
> [snip good info]
> > What does your program do?
>
> It reads in a large amount of data (a few million lines) and processes every 
> line by replacing certain strings with others based on a hash table. Then it 
> writes the reformatted data into a collection of about 300 files. So one big 
> file comes in and 300 smaller gzipped files go out.
>
> The C++ program reads the whole big file into memory, reformats it and writes 
> it out to 300 files, one at a time.  The Python program reads in the big file 
> one line at a time and writes each processed line immediately to one of the 
> 300 files, keeping all 300 open at once.
>
> The Python script surely uses minimal memory while the C++ program uses lots 
> of memory.  The Python program opens many files at once, but this seems not 
> to be a problem under most conditions, while the C++ file keeps open only one 
> output file at a time.
>
> Thanks for the tips, Stephen.
>
> Mike

I'm trying to account for the huge kernel time.  Is the file you read in 
very big?  Maybe the C++ program uses a lot of swap space on the drive. 
That would contribute to a huge kernel time.


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