Rebuilding RPMs results in bad update behavior
Dave Jones
davej at redhat.com
Wed Jun 13 03:41:04 UTC 2007
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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