Re: gfortran, g95, and dual-core

On 2007-09-30, Charles Russell <NOSPAM@xxxxxxxxxxxxx> wrote:
Richard Maine wrote:


So computing time is not simply a matter of counting "flops"

Nope. Hasn't been for decades.

For my present hardware, using a benchmark for "flops" that simply
multiplies large dense matrices, I have:

2/2003 desktop 100 Mflop/2.4GHz = 0.04 flop/Hz g77 with -fbounds-check
4/2006 laptop 40 Mflop/1.7GHz = 0.02 flop/Hz g77 with -bounds-check

Timing was not very accurate, done by stopwatch for portability of the
benchmark program, and these were short runs. The laptop, though newer,
is less efficient, presumably due to the factors you mention. It was a
low-end machine.

If the benchmark results above are representative of your real
application(s), you ought to be able to improve performance by more
than 1 order of magnitude without any new hardware. Dense matrix
multiplication of large matrices gets very close to the peak
performance of the processor, when using an optimized library, largely
due to better utilization of the cpu cache compared to a naive
implementation of the matrix multiplication algorithm. That is, your
2003 desktop should be able to do something close to 4 Gflops on
matmul.

--
Janne Blomqvist
.

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