[Sussex] Online with Ubuntu

[Geoffrey Teale]

Chris Jones wrote:
> For accelerating specific operations, typically floating point type
> operations. MMX/3DNow are only of any real use if you are hand coding
> assembly routines with them for things like codecs or 3D work. gcc isn't
> going to be able to do anything significant with them on most code.

gcc will use MMX and SSE register optomizations (for example) as 
appropriate, if ,and only if, the correct flags are passed to it.  You 
are right in saying that this kind of support only effects certain 
processes but nothing I have said prior to this point suggests otherwise.

Code for media application (like Theora) does take pains to use 
extensions like MMX to enhance performance if such things are available. 
  Getting this to work is not just as simple as turning the flag on in 
the  compiler, but passing the option to the configure script of the 
application.

Gentoo packages take care of all this.  Debian, even with some simple 
wrapper scripts will not because it's packages aren't designed to deal 
with complex sets of flags being passed to the config scripts.

> Do you have numbers? I've seen a lot of gentoo people claim a lot of
> things that nobody has managed to back up with actual data. Outside of the
> kernel and libc most things are going to be highly transport bound and all
> the optimistion in the world won't make your disks go any faster ;)

Firstly, there are several CPU specific optomisations that effect the 
throughput of I/O (though not directly disk access time).

Secondly, from experience a dual Xeon 2.4Ghz DNUK box with 1GB can 
render and detailed simulation of viral evolution and spread over a 
living cell group (representing a 12 year period) in roughly 2 days on 
an optomised build (done by hand, not Gentoo), but it takes more than 4 
days on an straight Debian woody build.

Quite an extreme example but my point was never that commmon usage was 
significantly faster on an optomised build, but there are specific cases 
where a distro like Gentoo is massively more appropriate than, for 
example, Debian.  I not trying to start Distro wars, but promote a 
sensible, reasoned approach to the recommendation and discussion of 
different distros.  One major advantage is open source is we have the 
choice to do it either way - the blind arguement that Debian can do 
anything if you want it to is pointless and counter productive.

It's worth noting that the same two builds take roughly the same time to
  do BLAST comparisons (which are predominantly disk and network based 
tasks).

> It's also worth noting here that Ubuntu's packages are not built for 386
> CPUs, they are built with P4 instructions, which, if anything will make
> the most difference when it comes to gcc flags.

Asolutely agreed.  Arch is equally built with i686 flags and works very 
well.  I use Ubuntu in the day to day and find it very very good.

--
Geoff Teale
Free Software Foundation <tealeg at member.fsf.org>