On Wednesday 08 September 2004 12:15, Klavs Klavsen wrote:
> Hi guys,
>
> Just read an interesting article about Xeon vs. Opteron from anandtech
> - where they really show how much difference compile optimizations (or
> not) does - and how it differs for different programs for different
> processors.
>
> http://www.anandtech.com/linux/showdoc.aspx?i=2163&p=1
>
> To me this clearly shows, that if Gentoo wants the best performance -
> we can't use a "one cflags fits them all" approach. I do know that if a
> program breaks, those CFLAGS are pulled out in the individual ebuild,
> but this is not due to poor performance.
>
> IMHO the only way for Gentoo to prove its true potential - is to
> somehow build an array of compile options, with CPU's on X, programs on
> Y and GCC-version on Z. Getting the numbers for each CPU, will ofcourse
> require writing tests, for each program - but IMHO this can be done, if
> we do it one at a time.
>
> I would suggest these tests be included like the gentoo-stats program,
> as something the individual Gentooist can choose to run after each
> compile - which would give him the optimal performance (and recompile X
> number of times to test different flags out) on his
> CPU/program/GCCversion combination, and at the same time, send the
> result to a Gentoo database.
>
> I know I would definetely have the patience to let it test and test
> again, if it meant more performance for me Smile
>
> The end result should be, that Gentoo automagically selects the optimal
> CFLAGS (in performance and stability - perhaps with some optimizations
> flagged as "unstable" so people can select "optimize for performance"
> vs. "optimize for stability") depending on the X, Y and Z from above.
>
> I would very much like to be one of the guys that gets the ball
> rolling, but as I'm not a Gentoo Dev - We (or just I) need to agree
> with the Gentoo Dev's on how this could best be done.
>
> What do you think? am I crazy? It seems to me that the anandtech tests
> shows that it is more than just a 1% or 2% difference, with the right
> CFLAGS - and that the right CFLAGS for one program, can be the worst
> for another on same CPU/GCC combination.

To do this for programs, one would need to have a realistic suite of 
"tests" that simulate the real world use of the application. Of course 
that also allows -fprofile_arcs to be used.

Paul

-- 
Paul de Vrieze
Gentoo Developer
Mail: pauldv@gentoo.org
Homepage: http://www.devrieze.net