Re: [gentoo-dev] Do we want optimal performance?

[Daniel Goller]

although i am against overly tweaking CFLAGS, someone suggested 
something that might be more sane to ask for:

/etc/portage/packages.cflags

an easy way to maintain your cflags you worked so hard for to obtain, 
you can trade them in the forums or ebay and then append to your file, 
not much work to implement in my eyes, and all the testing work is done 
by those who want it

this way those of you who want a per package set of CFLAGS get it w/o it 
being an impossible task for gentoo to implement

now you just need to get someone to make this happen or say "no, not 
even that will happen"

if the portage team picks it up, make sure to thank Magnade for the idea

Daniel


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.
>
>
>
>

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