[lug] Various Arch/Compiler Binaries living together

[rm at fabula.de]

On Sun, Jun 23, 2002 at 05:49:46PM -0600, Timothy C. Klein wrote:
> * Tom Tromey (tromey at redhat.com) wrote:
> > >>>>> "Ed" == Ed Hill <ed at eh3.com> writes:
> > 
> > Ed> Since then, I've become convinced that fussing with
> > Ed> platform-specific compilation and optimization tweaks is almost
> > Ed> always a waste of time.
> > 
> > Yeah, it is.  I think Red Hat compiles the kernel and glibc with
> > architecture-specific flags, but not anything else.  Unless the code
> > in question is very heavily used, the benefit is vanishingly small.
> > 
> 
> While I would not be overly surprised if you two are correct, I am not
> going to take your word for it :-)  If it is true, though, it would seem
> to imply the following:  the only difference between the i386 and
> Athlon/Pentium III/Pentium IV really boils down to clock speed (and I
> guess maybe memory bandwidth / cache size).  I am not sure I buy that.
> There *are* new, and more effiecent, instructions in the newer chips
> (3DNow, SSE, SSE2, MMX, etc..., to name those that have catchy names).
> So for the average application such things make no difference?

Yes, there are, but AFAIK you need _code_ support for those. For normal
appliocations there's really no need to optimize (on such a low level).
Unless you do  CPU-intensive comuptation or realtime stuff (image processing
or sound creation) it's not worth the time spent recompiling (have a look
at the output of 'top' to see how much "room" you've left on your CPU :-)
If you really want or need to speed up code it's often more rewarding to
optimize code/dataflow and data structure layout to get a more 'cache-friendly'
behaviour (i.e. you can get dramatic speedups if you memory access patterns
don't invalidate the second level cache all the time - and optimizing that
is something a human still is better at than a compiler ;-)

  Ralf Mattes

> Have any links to scientific analysis?
> 
> Tim
> --
> ==============================================
> == Timothy Klein || teece at silverklein.net   ==
> == ---------------------------------------- ==
> == "Hello, World" 17 Errors, 31 Warnings... ==
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