John Richard Moser
nigelenki at comcast.net
Tue Feb 8 16:03:01 CST 2005
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When GCC 4 comes out, switch to it ASAP (meaning when it doesn't break
crap), and start working with upstream on solving any problems it
causes. GCC 4 has SSA, and should be able to do better optimization.
Using -fssa on GCC <4 breaks everything in the universe, so don't do it.
Also, this isn't relavent for older machines, but GCC has a tendency to
use SSE instructions rather than 387 intrinsics to do math. SSE has
high overhead (Daed said 17 cycles to load an int or floating point to
an SSE register) and is suitable for heavy matrix calculation, but not
for much else. I always used -mfpmath=387 on Gentoo to force 387
intrinsics over SSE; this is likely only relavent on AMD64.
Along with -O2, -funit-at-a-time and -fweb can be used in GCC 3.4 and
up, which may prove to produce better results. I used these on Gentoo,
but never did real benches, so you're encouraged to test.
These two optimizations come from -O3; however, optimization levels
enable a set of switches AND some -Olevel specific changes. -O3 is
documented to enable all of -O2 plus -fweb -funit-at-a-time
- -finline-functions; but -O3 != -O2 -fweb -funit-at-a-time
- -finline-functions. I'm more inclined to avoid -O3 in favor of -O2
Never unroll loops. It's not worth it and "may make things slower."
Anyway, those're my suggestions.
Peter Damoc wrote:
> Except from this week's DistroWatch Weekly comments:
> • Re: Ubuntu's popularity (by Ariszló on 2005-02-08 08:43:33 GMT from
> Dexter Ang wrote: "1. Fast. It's not as fast as Gentoo, but it beats the
> hell out of Fedora."
> You must have a huge amount of RAM if you find Ubuntu fast. Try to
> install it on a machine with 128 MB of RAM and then compare Ubuntu with
> distributions like Slackware, Arch Linux, Yoper, Specifix or CCux.
> Beating the hell out of Fedora is not a big feat.
> I wanted to point this myself sooner.... as a goal for Grumpy maybe you
> could set up something like:
> Ubuntu Reviver.
> Same Ubuntu only a better selection of packages or compile flags so that
> older computers could be used.
> I don't want Ubuntu to run on 386 BUT a Pentium I MMX 166-200 with 64 Mb
> RAM could be a nice target.
> You gave people something to replace WinXP now give them something to
> replace Win 95.
> A lot of older computers get parked in third world countries as part of
> donations... these systems need something to run...
> Most of these computers come with no licence for Windows... and they run
> solely because there is a tacit acceptance from competent authorities...
> but that won't last forever.... and soon schools might have to uninstall
> Windows... because they won't be able to find money for licences. They
> might end up closing the laboratories because... linux enthusiasts
> willing to give a try to "DeLi Linux" or whatever works on these
> systems, are in short supply and there might not be anyone to help them
> out of the mess.
> Of course there is a chance, a big chance, that even users with higher
> level systems might end up using such a version. ;)
> I for one would love to see a version based on Rox or IceWM. ;)
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Creative brains are a valuable, limited resource. They shouldn't be
wasted on re-inventing the wheel when there are so many fascinating
new problems waiting out there.
-- Eric Steven Raymond
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