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geoffs
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Joined: 15 Feb 2003
Posts: 35
Location: Canada

PostPosted: Mon Mar 03, 2003 8:51 am    Post subject: Gentoo-sources kernel oddities Reply with quote

I decided to give the gentoo sources kernel a go today. Everything went ok (i guess) and when it was all said and done I noticed 2 strange things.

The gentoo-sources kernel is about 100k bigger then my old 2.4.20 vanilla kernel (same config)... AND my system lost 25 bogomips with the gentoo-sources kernel. Now 25 bogomips might not sound like a lot, but I find it odd that the "optimized" kernel would have this effect.

My machine is a dual celeron system...does SMP have anything to do with this?
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geoffs
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Joined: 15 Feb 2003
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Location: Canada

PostPosted: Thu Mar 06, 2003 5:32 am    Post subject: Reply with quote

ttt

someone else must have this problem
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max_colby
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Joined: 30 Nov 2002
Posts: 149
Location: Ottawa, Canada

PostPosted: Thu Mar 06, 2003 6:28 am    Post subject: Reply with quote

Gentoo sources compiles itself with -O3 while all other kernels I've tried compiled with -O2. That explains the increased code size (due to code inlining).

As for lost bogomips, some patches slightly decrease the peak performance of certain things in favour of responsiveness and a faster 'feel', since many of the patches are aimed at desktop users.

Also, most of what I've read, and my own experience has supported that -O2 creates faster code than -O3, so this might have something to do with it; I'm not sure about the kernel compilation specifically though. I'm not sure how to get gentoo-sources to compile at a lower level either .. hopefully somebody can fill me in.
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max_colby
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Tux's lil' helper


Joined: 30 Nov 2002
Posts: 149
Location: Ottawa, Canada

PostPosted: Thu Mar 06, 2003 6:46 am    Post subject: Reply with quote

As for changing the kernel compilation options, this has come up in another thread:
https://forums.gentoo.org/viewtopic.php?t=5717&start=325

All you have to do is edit line 20 of the kernel Makefile
Code:
nano /usr/src/linux/Makefile -w


I really wouldn't recommend changing anything other than the -O* value though
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