Optimisation

Chris Gianelloni twi at faradic.net
Tue Sep 5 11:46:38 PDT 2000


peter.wood at worldonline.dk wrote:

>
> I compiled everything (as far as I remember, ha, ha) with "-O3 -mcpu=i586
> -march=i586", on an AMD K6 233Mhz and everything works (so far).  And my answer
> to the question "Why go to the trouble of bothering with optimisation?" is
> "Because I can."  Just like some car freak might tune his vehicle endlessly,
> for insignificant performance gains, or maybe even performance losses!  I like
> fiddling with my software (sounds disgusting doesn't it?) so I do.
>
> Peter

I know exactly what you mean.  I use my linux as my only operating system.  I have
dual CPUs, which are Pentium III's... so my kernel has p3 patches in it.  I use
PMesa instead of regular Mesa because it is parallel (and has SSE support).  I use
pgcc because it compiles code that is better optimised for pentium (and up) class
machines.  I replaced the 3Com NIC driver in my kernel with the parallel version.
The reason I was turned onto LFS (I have been using Slackware) was twofold: one -
I don't get all kinds of crap I don't need... two - I can optimise it much better
than a distribution will.

Does optimisation make a difference?

I have compiled my kernel under pgcc with both the default "-O2 -m486" and "-O6
-march=i686".  Both produced perfectly fine, bootable, working kernels.  The one
with higher optimisations boots *noticeably* faster, which is reason enough for me
to use it.

Milliseconds may not make a difference to you, but to me those milliseconds add
up.  How many "only milliseconds" a day am I saving when you add them all up?  I
really don't know...  but I am sure that it is substantial enough to be worth the
extra time to me.

Now..... if ftp.slackware.com (the only place I have seen generic patches against
glibc) will freaking change the permissions on their glibc source so I can
download those fixes, I'll be ready to roll on.

I am keeping track of what packages do and don't like optimisation, so I'll post
my findings for whomever would like to see them.  I am building all of my static
build with the default optimisations.






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