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gentoo-fan
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 Posted: Fri Jun 14, 2002 8:47 pm Post subject: Compile 2.4.18 Kernel with -O3 -pipe? |
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Is it a good idea to compile the Kernel
(e.g. 2.4.1 with the -O3 -pipe flags?
Thanks!
gentoo-fan |
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maystorm
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Joined: 02 Jun 2002
Posts: 222
Location: Germany, not far away
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| Posted: Sun Jun 16, 2002 12:31 am Post subject: |
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Most probably not... not sure, though... don't want to be a dead hero, either... 
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AlterEgo
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Joined: 25 Apr 2002
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| Posted: Sun Jun 16, 2002 1:30 pm Post subject: |
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| Never had any problems with it. |
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dmmgentoo
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Joined: 16 Jun 2002
Posts: 38
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| Posted: Sun Jun 16, 2002 7:26 pm Post subject: |
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| I'd recommend no higher than -O2. I think it's counter-productive to use -O3, because it inlines everything in sight. This bloats the code, and causes the apps to consume more memory. Surely, you want the kernel to be as small/fast as possible? I think -O2 is the safest bet, unless you absolutely positively need to squeeze every once of performance out of the app you're compiling. Also, remember that higher optimization levels lead to longer compile times. |
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Vanquirius
Retired Dev
Joined: 14 Jun 2002
Posts: 1297
Location: Ethereal plains
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| Posted: Sun Jun 16, 2002 8:19 pm Post subject: |
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| works fine here |
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thomson
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Joined: 01 Sep 2002
Posts: 25
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| Posted: Sun Sep 01, 2002 8:12 pm Post subject: optimization flag not transmitted into kernel? |
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I have CFLAGS in my /etc/make.conf set to -march=pentium -O3 -pipe for a laptop I'm compiling a system on.
I'm using the gentoo-sources 2.4.19-r7
when I'm compiling the kernel (make clean dep bzImage modules) I see the -march=pentium flag is being passed, but the -O stays at -O2.
Any idea what's happening here? Or, since I'm not doing the compile via emerge, do I need to go in and change each of the Makefiles in the linux tree?
thx! |
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rac
Bodhisattva
Joined: 30 May 2002
Posts: 6553
Location: Japanifornia
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| Posted: Sun Sep 01, 2002 8:20 pm Post subject: Re: optimization flag not transmitted into kernel? |
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| thomson wrote: | | Any idea what's happening here? Or, since I'm not doing the compile via emerge, do I need to go in and change each of the Makefiles in the linux tree? |
CFLAGS don't affect kernel compilation. The kernel in my experience has good reasons for choosing what compiler flags it is compiled with, and I would recommend leaving it alone. That being said, if you really want to change things, | Code: | | $ make bzImage CFLAGS_KERNEL="-O9 -fgo-crazy" |
...might be what you are looking for. If you do decide to go this route, and you have problems with instability or anything, please make sure that the problem persists even with the kernel compiled with default optimizations before reporting bugs.
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thomson
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Joined: 01 Sep 2002
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| Posted: Sun Sep 01, 2002 8:24 pm Post subject: |
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| thank you! will give it a try, but still keep the default kernel in /boot and grub jic. |
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sn1987a
n00b
Joined: 30 Aug 2002
Posts: 26
Location: Houston Tx
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| Posted: Mon Sep 02, 2002 12:07 am Post subject: |
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According to "Documentation/Changes":
| Quote: | In addition, please pay attention to compiler optimization. Anything
greater than -O2 may not be wise. |
Having said that, the gcc man page indicates that the only difference between -O2 and -O3 is that -O3 includes -finline-functions. The kernel is already very carefully inlined. The compiler may not find additional candidates for inlining.
There is usually a reason for the code in the kernel to be setup in a certain way and you may not want the compiler second guessing the developers. |
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helmers
Guru
Joined: 16 Sep 2002
Posts: 553
Location: Stange, Norway
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| Posted: Fri Sep 20, 2002 8:27 am Post subject: |
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Would it be possible to add "march=athlon-xp" in here? And will it then make use of sse?  |
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de4d
Apprentice
Joined: 12 Sep 2002
Posts: 181
Location: fr. i. br. (ger)
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| Posted: Fri Sep 20, 2002 8:45 am Post subject: |
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| helmers wrote: | | Would it be possible to add "march=athlon-xp" in here? And will it then make use of sse? :o |
--march=atlon-xp works fine for me (gcc 3.2r1, kernel2.4.19r9)
i cannot promise this is using sse, but i think so
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Installing Gentoo
