Re: Slow performance on Linux

[Jim Van Zandt]

My results on a 90 MHz Pentium:

Octave, version 1.1.1.
Copyright (C) 1992, 1993, 1994, 1995 John W. Eaton.
This is free software with ABSOLUTELY NO WARRANTY.
For details, type `warranty'.

octave:1> bm
parse error near line 79 of file bm.m:

>>>

    ^

warning: comma in global declaration not interpreted as a command
separator
test #1          0.23125 +/- 3.1% (10 runs)
test #2           1.2576 +/- 5.0% (102 runs)
test #3         0.062327 +/- 13.6% (1000 runs)

...about twice as long for the first two tests, and over 100 times as
long for the third test.

The parse error was generated by the formfeed.

In message <address@hidden>, Francesco Potorti` writes:
>It takes 8s per test on alpha.  If the time does not converge, it will
>iterate as much as 1000 times, that is 8000s (2 and half hours) on
>alpha.  Set the maxrepetitions variable in bm.m to 100 (it is
>currently set to 1000), which is probably a more reasonable value.

I think it makes more sense to limit the total *time* (to perhaps 100
sec) rather than the number of repetitions.  That lets you use the
same benchmark over a wider range of machines, and continue to use it
as machines speed up.

We might also think about scaling up the size of the problem rather
than the number of iterations.  (As machines get more powerful, we
tend to tackle bigger problems rather than just answering the same
size problems in less time.  This is what makes Amdahls' Law mostly
irrelevant.)  Of course, the scaling has to be understood.  If the
benchmark were "the biggest matrix that can be inverted in 60 sec",
then doubling the size of the matrix takes 8 times the processing
speed.  The "doubling" doesn't sound as impressive as the factor of 8,
though.

                          - Jim Van Zandt