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Re: Rebuilding RPMs results in bad update behavior



On Tue, Jun 12, 2007 at 09:41:58PM -0500, Callum Lerwick wrote:
 > On Wed, 2007-06-13 at 04:28 +1000, Mike Kearey wrote:
 > > I'd like to see repeatable, measurable tests not subjective 'I think
 > > it's faster' observations. I am no criticizing here, it's just that
 > > humans are actually bad at this sort of thing. Measurements are better.
 > 
 > I've been doing rather extensive performance profiling on OpenJPEG,
 > using Fedora 6/7's gcc 4.1, and I've discovered a few things:
 > 
 > Compiling for pentium3 rather than "generic" measurably improves
 > performance on both my i386 test platforms, mobile Celeron 1.3 (PIII
 > based), Celeron 2.1 (P4 based). This is at least partly due to
 > optimizing signed integer math with cmovs.

No surprise really.
generic isn't targetting either of the processors you mention.
The idea behind generic is 'optimise for _todays_ CPUs', which
right now typically means Intel Core, and AMD Opteron/Athlon64.
On these platforms, cmov isn't a win (and is even a loss in
some cases).

For stuff that's really performance sensitive, runtime selection
of optimised routines is a far better solution than n different
packages for each flavour of CPU.

	Dave

-- 
http://www.codemonkey.org.uk


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