On Nov 18, 2011 10:41 PM, "Fredric Johansson" <fredric.miscm...@gmail.com> wrote: > > On Wed, Nov 16, 2011 at 2:58 PM, Pandu Poluan <pa...@poluan.info> wrote: > > > > On Nov 16, 2011 2:26 PM, "Michael Mol" <mike...@gmail.com> wrote: > >> > >> On Wed, Nov 16, 2011 at 2:11 AM, Stéphane Guedon < steph...@22decembre.eu> > >> wrote: > >> > On Wednesday 16 November 2011 02:07:12 Pandu Poluan wrote: > >> >> And if you're adventurous, add USE "graphite", reemerge gcc, and > >> >> reemerge > >> >> world :) > >> > > >> > what does "graphite" add ? > >> > >> Thanks for reminding me; I meant to look it up when I got home. > >> > >> shortcircuit:1@serenity~ > >> Wed Nov 16 02:16 AM > >> !501 #1 j0 ?0 $ euse -i graphite > >> global use flags (searching: graphite) > >> ************************************************************ > >> no matching entries found > >> > >> local use flags (searching: graphite) > >> ************************************************************ > >> > >> [snip] > >> > >> [- ] graphite > >> sys-devel/gcc: Add support for the framework for loop optimizations > >> based on a polyhedral intermediate representation > >> > >> So, a new, experimental optimization model and framework inside your > >> compiler. If it's specifically for optimizing on loops, I'll venture a > >> guess it's going to be mostly effective for graphics libraries and > >> apps. I've got some slightly riskier educated guesses on how it works > >> and what some numeric side effects and consequences might be, but they > >> scare me, so I think I'll leave it to someone who actually knows more > >> about it... > >> > > > > I've been using USE "graphite" since gcc-4.5.3-r1 appeared. Upstream says > > that graphite is stable, feature-complete, and production-ready since 4.5.3. > > > > To fully taste the effect of graphite, I even went the torturous route of > > emerging gcc + libtool + binutils (in that order) twice, followed by a > > wholesale-rebuild of everything (emerge --emptytree), then tarballed the > > result to my own "stage3.1" tarball to spare me the *huge* amount of time > > required. > > > > I've deployed 3 systems with USE "graphite", and they *felt* snappier. > > emerge's *felt* slower, though. (no objective tests, I know). > > > > I use Gentoo as a gatewall, and there I did a wholesale-rebuild one more > > time, this time specifying CFLAGS "-march=native"... and I just couldn't be > > happier with the resulting performance :-) > > > > Rgds, > > > > I might be wrong but don't you need to have the gcc's options for > graphite enabled to actually make use of the graphite framework? (You > might be using them but you haven't mentioned it.) >
Yes. There are some CFLAGS incantations to add to fully utilize graphite, else the optimizations would be marginal at best. That said, turning on the CFLAGS flags was a *very* involved process: 1. By default, "graphite" is disabled. So you can't directly turn on the graphite-related CFLAGS option. You must first enable USE "graphite" and re-emerge gcc (or upgrade, if you're still using <gcc-4.5.3). This will pull in ppl and cloog-ppl. 2. I don't know if libtool and binutils need to be remerged, but I did it just to be safe. 3. Now that gcc has been compiled with graphite support, you can turn on the CFLAGS flags necessary to fully utilize graphite. WARNING: some flags recommended by upstream *might* make some programs run worse; be careful. (I won't have access to my servers so I can't tell you which ones exactly). 4. At this point, I want gcc itself to be optimized. So, I remerged gcc and libtool and binutils (in that order). Might be unnecessary, but I'm anal like that :-) 5. Finally, universe-remerge (emerge --emptytree). As you can see, steps 4 & 5 are optional. And they indeed took a *humongous* time to complete. But I am quite satisfied with the result. Everything felt snappier compared to older boxen that haven't been graphite-ed :-) Of course, YMMV. Rgds,
