Re: Optimization levels when compiling PostgreSQL...
От | Sean Chittenden |
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Тема | Re: Optimization levels when compiling PostgreSQL... |
Дата | |
Msg-id | 20020910153030.GD26147@ninja1.internal обсуждение исходный текст |
Ответ на | Re: Optimization levels when compiling PostgreSQL... (Neil Conway <neilc@samurai.com>) |
Список | pgsql-hackers |
> > Agreed, however some of the loop-unrolling might prove to have some > > optimization, but we'll see. I'd like to think that there's some > > actual value in -O6 beyond the geek appeal of being able to say it's > > been compiled with all the optimizations possible. ::shrug:: > > BTW, -O3 is the highest GCC optimization level; anything higher than > that is synonymous with -O3, I believe. Also, -O3 doesn't have > anything to do with loop unrolling, AFAIK. In terms of instruction optimization, yes. Above that is where it does the loop unrolling, inlining, and other various tweaks. > As for the value of enabling that flag, it depends IMHO on the > performance gain you see. If there is a significance difference, let > -hackers know, and it might be worth considering enabling it by > default for certain platforms. If the performance difference is > negligible (which is what I'd suspect), I don't think it's worth the > code bloat, reduced debuggability, or the potential for running into > more compiler bugs. Agreed. Later today I'll thump on my good SCSI system and let you know what happens. > Also, if -O3 *is* a good compiler option, I dislike the idea of > enabling it for your own packages but no one else's. IMHO > distributors should not futz with packages more than is strictely > necessary, and a change like this seems both unwarranted, and > potentially dangerous. If -O3 is a good idea, we should make the > change for the appropriate platforms in the official source, and let > it get the widespread testing it requires. Agreed, but the testing's got to start someplace. :~) The -O3 is a tunable that you can optionally set or unset so it's not like I'm forcing it to be on (thought it will by default for the -devel port). -sc -- Sean Chittenden
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