performance tuning differences?

Jakob Østergaard jakob at unthought.net
Tue Aug 14 10:58:46 EDT 2001


On Tue, Aug 14, 2001 at 10:01:16AM -0400, Dan Kirkpatrick wrote:
> Any suggestions on pure performance tuning?  Maybe some things to look into?

Tuning what ?

Can you be more specific ?   What did you try ?  What does your profile
information say ?    Any ideas of what might be taking up the time ?  Is this a
parallel application ?   Is it threaded ?  Is it heavy on FP or integer ?

> I'm sure it's "everything" but are there any tricks that have been fairly 
> painless and resulted in good return?

Use good algorithms.  Implement them well.

Use the right language for the job.  And the right compiler for the language.

Instrument the code, and measure, and measure, and measure.

Avoid cache misses by ensuring good data locality in your algorithms (no,
you're not running on a John von Neumann architecture - that was 20 years ago -
the memory system is hierarchical these days)

Understand the problem, and how you're solving it.  Then understand your
computing architecture.  Change the way you solve the problem to take
advantage of your architecture.

> 
> We're benchmarking different platforms, some of which with the same hard 
> drive/memory/chipset/processor speed, network inconsequential, etc... with 
> more than subtle differences.

I've had an 80 MHz vector machine outperforming an almost linearly scaling
parallel implementation of the same problem running on *seven* 180 MHz SP/2
nodes.   This was because of cache.

And I've had my PPro 150 run rings around the 180 MHz Power2 nodes on another
problem that didn't use FP.

Architectures differ - that's the beauty of it all   :)

> 
> Just the difference of installing straight RedHat Linux 6.2 vs 7.1 has 
> resulted in 5%-20% performance differences depending on code, the higher 
> difference being floating point calculation code.

Newer kernel, better performance for most problems.

> 
> Just wondering what the consensus is for major things to try or avoid.

Avoid whatever is slowing down your code - that's about as specific as
I can get, given the level of detail in your mail   :)

-- 
................................................................
:   jakob at unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:

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