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supermihi
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Joined: 09 Feb 2005
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 Posted: Sun May 28, 2006 7:58 am Post subject: kdeenablefinal - when does it make sense? |
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Hi,
I am currently compiling KDE on a 800MHz Duron ith 256MB RAM. Nobody is working on that machine, so I wonder if it made sense to enable the "kdeenablefinal" USE-Flag for the emerge. Or is this only recommendable with more RAM?
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lonex
Tux's lil' helper
Joined: 22 Aug 2004
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Location: Karlsruhe, Germany
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| Posted: Sun May 28, 2006 9:53 am Post subject: |
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kdeenablefinal only makes sense when you have at the very least 512mb ram. even then, it sometimes starts to swap like mad, so i strongly advise against using it with only 256mb of ram.
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lost+found
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Joined: 15 Nov 2004
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Location: North~Sea~Coa~s~~t~~~
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| Posted: Mon May 29, 2006 5:27 am Post subject: |
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| Quote: | /usr/portage/profiles/use.desc:
kdeenablefinal - Makes kde ebuilds use the enable-final flag, yielding big compilation speedups at the cost of very heavy mem usage |
| Quote: | kdeaddons-3.5.0.tar.bz2, configure:
--enable-final build size optimized apps (experimental - needs lots of memory) |
...but, at the cost of what else? Does it need more RAM at compile time only, or at runtime too?
Building "size optimized apps" looks like using -Os to me. :-S
Cheeeers. |
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supermihi
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| Posted: Mon May 29, 2006 5:51 am Post subject: |
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afaik it needs a lot of memory during compile time at the cost that you'r almost not able to use your compuer while it compiles. It loads the whole package into memory and compiles it as once, instead of linking the various programs together.
By doing this it is also possible to create more efficient, smaller binaries. So, if you have enough mem, you should really enable this flag.
This is what I heard, but currect me if I'm wrong.
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Hum
Tux's lil' helper
Joined: 13 Oct 2005
Posts: 116
Location: Canada
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| Posted: Mon May 29, 2006 6:03 am Post subject: |
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| Quote: | --enable-final:
Concatenates all .cpp files into one big .all_cpp.cpp file, and compiles it in one go, instead of compiling each .cpp file on its own. This makes the whole compilation much faster, and often leads to better optimised code, but it also requires much more memory. And it often results in compilation errors when headers included by different source files clash one with the other, or when using c static functions with the same name in different source files.
This is a good thing to do at packaging time, but of course not for developers, since a change in one file means recompiling everything. |
Source: http://developer.kde.org/documentation/other/developer-faq.html |
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lost+found
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| Posted: Mon May 29, 2006 6:38 am Post subject: |
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Thanks.
I think I will try it, booting up non graphical, 320 MB RAM + 2 x 512 MB SWAP in parallel on separate drives...
HA hA The monolithic ebuilds. Just for fun...  |
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lost+found
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| Posted: Wed May 31, 2006 10:04 am Post subject: |
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| lost+found wrote: | Thanks.
I think I will try it, booting up non graphical, 320 MB RAM + 2 x 512 MB SWAP in parallel on separate drives...
HA hA The monolithic ebuilds. Just for fun... |
Wow, this cuts off 30-40% compilation time. I saw no swapping at all, so I decided to continue compiling with xorg/kde running. Then I saw a small increase of swapspace usage. I guess some unused files from other processes...
Cheeeeeeeers.
Last edited by lost+found on Wed May 31, 2006 12:28 pm; edited 1 time in total |
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Massimo B.
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Location: PB, Germany
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| Posted: Wed May 31, 2006 10:31 am Post subject: |
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I didn't notice swapping and the 640M physical ram were about 70 percent used. I just use this machine as usual under KDE while emerging with "kdeenablefinal" (PORTAGE_NICENESS="5").
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Torangan
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Joined: 21 Mar 2003
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| Posted: Wed May 31, 2006 3:48 pm Post subject: |
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| Don't forget that this also opens up further optimization possibilities. A huge group of files is clumped together and since 3.4 GCC does have -funit-at-a-time (implied by -O2) which performs optimizations over the whole compilation unit. Using this option more code is put into one file so GCC does have more possibilities. Most intersting could be -O3 since more code in one unit means more potential for inlining. |
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