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reconfiguring and compiling kernel, why so long time?
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genter
n00b
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Joined: 30 Nov 2014
Posts: 2

PostPosted: Sun Nov 30, 2014 1:35 pm    Post subject: reconfiguring and compiling kernel, why so long time? Reply with quote

Hi all, I use gentoo for quite a few years. These days, I get a new gentoo mini iso and install it to my new notebook. I'm trying to adjust the kernel configuration, the steps are just as:

# cd /usr/src/linux
# make menuconfig
# make && make modules_install
# make install

It takes 2 or 3 hours first time, that's normal to me. But later on, each time when i reconfigure the kernel and then recompile the kernel, it still take so long time! it recompiles every kernel source file again! that's not the case as my old experiences, why?

thanks!
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ShanaXXII
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Joined: 29 Jun 2014
Posts: 283
Location: Canada

PostPosted: Sun Nov 30, 2014 2:12 pm    Post subject: Reply with quote

This happens to me too.
I think it all depends on how you changed the configuration.
Sometimes, my kernel recompiles very quickly, sometimes it recompiles the whole thing.
:/
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genter
n00b
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Joined: 30 Nov 2014
Posts: 2

PostPosted: Tue Dec 02, 2014 8:23 am    Post subject: Reply with quote

Yes, after 3 or 4 times of reconfiguring and recompiling, the process of make is fast as expected, and doesn't compile every compiled source file any more.

Thank you, Shana.
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Chiitoo
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Joined: 28 Feb 2010
Posts: 1802
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PostPosted: Fri Dec 05, 2014 8:57 am    Post subject: ><)))°€ Reply with quote

I believe different changes have different effects on what needs to be rebuilt (and many would probably suggest doing a make clean anyblue), but in any case, I took notice of your make-command example having no jobs-number defined. If one has more than one CPU-core, one might probably like to look into the -j (--jobs) option of make.

For example here, with -j6 on a 6-core Phenom, building linux-3.17.4-ck just now on the side while some of my usual CPU-utilising thingies like games and such are running:

Code:
real    3m21.653s
user    13m39.721s
sys     1m0.048s

With -j12:

Code:
real    2m52.875s
user    13m59.219s
sys     1m0.779s

As to why you would notice a difference compared to the past, I can only guess.
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katfish
Tux's lil' helper
Tux's lil' helper


Joined: 14 Nov 2011
Posts: 147

PostPosted: Fri Dec 05, 2014 8:58 am    Post subject: Re: reconfiguring and compiling kernel, why so long time? Reply with quote

# make --jobs (sum of cpu cores +1); make modules_install --jobs (sum of cpu cores +1)

should speed up compilation time ;)
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Ant P.
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Joined: 18 Apr 2009
Posts: 5878

PostPosted: Fri Dec 05, 2014 3:42 pm    Post subject: Reply with quote

If you change something like the memory management options, the entire kernel depends on that so it'll all need to be rebuilt. Adding a single device driver won't.
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