El Mie, 4 de Febrero de 2009, 7:17, Grant Edwards escribió: > On 2009-02-04, James <wirel...@tampabay.rr.com> wrote: > >> Grant Edwards <grante <at> visi.com> writes: >> >> >>> Whenever I see a write-up of Gentoo, it's described as a system >>> similar to BSD "ports" where you build packages from source. The main >>> benefit claimed for this approach is that you get better performance >>> because all executables are optimized for exactly the right >>> instruction set. is practically nil in real-world usage. >> >> Not true. You can eliminate many non-essential portions of a >> compiled program, via use flag and the freedom you get to select >> software, as opposed to other distros. Smaller executables are usually >> always faster. > [...] > But that wasn't what I was talking about, and AFAICT that's not > what reviewers are talking about when they talk about adjusting compiler > flags to optimize performance. They seem to be talking about building for > Athlon instead of P4 (or vice-versa). > Perhaps I've always completely misunderstood the articles I've > read, and they were indeed talking about USE flags that control options > passed to "configure" and not about things like gcc's -march and -O > options.
USe flags can be used for anything. Note that ebuilds are ultimately bash scripts. And USE flags are just that: f-l-a-g-s. Flags are used in a script to control things that can be run -or not- depending on a condition, things like "if in amd64 do this, if not, if hardened do that, if yes and hardened to anything else"... That includes things like activating concrete portions of arch dependent code or a patch, things like passing a simple option to add or remove a dependency, and any other things that you could do manually on a shell. It can of course be used as well to adjust CFLAGS and other things depending on the architecture or whatever condition you want. And even more, they can be used to filter CFLAGS that the developers know that are harmful (and that's a big part of the portage stability, because in the past users used to shot themselves on the feet by adding a 20 lines long CFLAGS declaration into their make.conf's. Note that reviewers usually test a thing for 2 days, and then they think they are qualified to talk about whatever thing. Some times, these reviews are useless for this reason. They only scratch the surface, giving a bad impression or just a poor one. Note that I said "some times", though I think that "most times" is potentially a more correct qualifier. -- Jesús Guerrero
