From: Isaac Gouy <igouy@...>
Date: 2006-08-02T05:00:07+09:00
Subject: Re: For performance, write it in C - Part 3, Source code now available


Thomas E Enebo wrote:
> On Wed, 02 Aug 2006, Charles O Nutter defenestrated me:
> >
> > First, some notes on benchmarking:
> >
> > - NEVER include IO when benchmarking a numeric algorithm; IO speeds vary
> > greatly from system to system and can vary from run to run depending on what
> > else is happening
>
>   IO can be noisy. I say avoid it for any benchmarking since it can
> greatly influence timings.  Usually the IO is not what you want to
> measure so why add this variable into things?
>
> > - If you're building up a large chunk of strings, write to an internal
> > buffer and then write out at the end; don't write for every little tiny
> > operation. At the very least, use a buffer per-line, rather than a separate
> > write for every element on that line.
>
>   I just informally thought I would measure a few things involving IO.
> I only changed the printing and nothing else:
>
> Unaltered test: ~3.8s
> Use of StringBuffer to print out a single row: ~2.1s
> Use of StringBuffer for entire run: ~1.5s
> Preallocated StringBuffer for entire run: ~1.4s
>
>   As you can see IO can have a large affect on clock time.  I demonstrated
> that in Java's case the IO in the benchmark accounted for over 2/3 of the
> wall clock time (which is interesting because a decent chunk that is
> left over is JVM startup overhead).
>
> Some stack allocated space will likely improve the C run as well (and in
> this case you can output it in a single write system call).
>
> -Tom
>
> --
> + http://www.tc.umn.edu/~enebo +---- mailto:enebo@acm.org ----+
> | Thomas E Enebo, Protagonist  | "Luck favors the prepared    |
> |                              |  mind." -Louis Pasteur       |


As you're having so much fun, let me suggest you try converting the
OutputStrings to byte-arrays, and pre-allocating a byte buffer for
output like the approach taken with this program
http://shootout.alioth.debian.org/gp4/benchmark.php?test=fasta&lang=java&id=2