Re: [Boost-users] Efficiacy of std::vector

From: Dave Steffen (dgsteffen_at_[hidden])
Date: 2006-08-28 12:57:24

Brian Budge writes:
 > This is most likely that you are not getting your operator[] inlined.
 > The function call overhead for such a small operation is going to be
 > very large.  Optimizations are your friends.
 > On 8/26/06, Janos Vegh <vegh.janos_at_[hidden]> wrote:
 > >
 > >
 > >
 > > On 8/26/06, me22 <me22.ca_at_[hidden]> wrote:
[...]

 > > > Empty cycle
 > > > real    0m0.003s
 > > > user    0m0.000s
 > > > sys     0m0.000s
 > > >
 > > > STL=1, SIMPLE=1, size=1000
 > > > real    0m1.357s
 > > > user    0m1.168s
 > > > sys     0m0.008s
 > > >
 > > > STL=1, size=1000
 > > > real    0m1.337s
 > > > user    0m1.172s
 > > > sys     0m0.016s
[...]

A comment on this sort of thing: using a shell's "time" is merely an
OK way to measure performance -- OK, but not great.

I strongly suggest that the OP, and anybody else interested in such
things, go get a recent verson of valgrind.  The 'callgrind' tool
counts the number of instructions execuded, which is a much more
accurate and reliable measure.  Also, get kcachegrind (a plug-in for
KDE); together with callgrind, it'll tell you instruction counts on a
line-by-line basis.  (The usual caveats apply.)

If you can't use valgrind on your platform, then I strongly suggest
you aquire some other good profiling tool, such as VTune.

Trust me, you'll get much, much better and more consistent results
this way.

----------------------------------------------------------------------
Dave Steffen, Ph.D.      
Software Engineer IV              Disobey this command!
Numerica Corporation                 - Douglas Hofstadter
dgsteffen at numerica dot us