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wichtounet
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Joined: 17 Mar 2012
Posts: 65

PostPosted: Tue Jun 18, 2013 7:32 am    Post subject: Can I change my processor without reinstalling ? Reply with quote

Hi,

I will soon upgrade my configuration (motherboard,ram and processor).

I would like to know if it is possible without reinstalling everything. I don't mind recompiling everything as it can run when I'm at work, but I do not want to reinstall everything.

I have an old Core 2 Duo and my system is compiled with march=native. I will upgrade to a new Haswell i7.

What I want to do is:

With the old processor:
Remove march=native
Recompile everything

With the new processor:
Set march=native again
Recompile again everything

Can something like that works ?

Thanks
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DawgG
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Joined: 17 Sep 2003
Posts: 595

PostPosted: Tue Jun 18, 2013 8:42 am    Post subject: Reply with quote

as long as you don't change ARCH i think it should be possible to just boot the "old" system with a rescue-cd, then chroot into it and do sth. like
Code:
emerge -eD world

if you change the motherboard/hardware you have to configure the kernel accordingly.
of course, when doing major changes like that it's mandatory to have backups of EVERYTHING before even trying anything.
GOOD LUCK!
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Maitreya
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Joined: 11 Jan 2006
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PostPosted: Tue Jun 18, 2013 9:29 am    Post subject: Reply with quote

I don't think gcc has a lot of different optimizations that make native/core2 compilations as opposed to native/core-avx2 that would make it incompatible to run.
Maybe not as efficient.

Try to boot it as it will probably JustWork™

If it doesn't; Like DawgG said : keep your install somewhere safe
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bbgermany
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Joined: 21 Feb 2005
Posts: 1437
Location: Oranienburg/Germany

PostPosted: Tue Jun 18, 2013 10:00 am    Post subject: Reply with quote

Hi,

According to this: http://ark.intel.com/compare/27258,35428,35605,75125 the latest core2 compared to haswell i7 they only added features. so you should be fine. I would say, if you go with amd instead of intel you need to remove -march=native with recompiling everything before moving.

bb
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chithanh
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Joined: 05 Aug 2006
Posts: 1561
Location: Berlin, Germany

PostPosted: Tue Jun 18, 2013 6:11 pm    Post subject: Reply with quote

Yes, i7 has a superset of core2 instructions.
But even when not (e.g. switching from and to Atom, or between Intel and AMD), you can set generic CFLAGS and "emerge -e @system" on the old CPU, then set -march=native again and "emerge -e @world" on the new CPU.
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wichtounet
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Joined: 17 Mar 2012
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PostPosted: Wed Jun 19, 2013 6:43 am    Post subject: Reply with quote

Thanks a lot for all your answers :)

I will try first without changing anything to see if it works and then recompile again to profit from the latest instructions. I'll come back here if I have problems ;)
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mattst88
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Joined: 28 Oct 2004
Posts: 362

PostPosted: Wed Jun 19, 2013 9:48 pm    Post subject: Reply with quote

There are only new instructions from your old CPU to Haswell. It will just work without rebuilding everything. Don't waste your time.
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