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fieryred2k
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Joined: 23 Mar 2004
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 Posted: Mon May 10, 2004 6:08 pm Post subject: A Hardware upgrading question... |
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I wasn't sure if this is the place to put this, but it seemed as good as any. I'm planning to upgrade my mobo/processor from a p3 550 to an amd athalon 2400+, my biggest concern is what that will do to my gentoo installation.
I understand that I would have to recompile the kernel, that's a given. My concern is all the software, that I compiled -march=pentium3, will I have to recompile everything? I've taken quite some time to compile the software and I really don't want to have to go through that again... will the binaries compiled with -march flag work on other processors that have been released later? or will the fact that I'm changing not only processor generations but also brands cause me more problems than it's worth? any help would be greatly appreciated
Last edited by fieryred2k on Mon May 10, 2004 6:13 pm; edited 1 time in total |
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Voltago
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Joined: 02 Sep 2003
Posts: 2593
Location: userland
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| Posted: Mon May 10, 2004 6:11 pm Post subject: |
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| Yes, you'll have to recompile everything, since the --march cflag breaks compatibility with other processor families. |
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YopWongSapn
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Joined: 26 Jan 2004
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| Posted: Mon May 10, 2004 6:12 pm Post subject: Re: A Hardware upgrading question... |
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| fieryred2k wrote: | | I'm planning to upgrade my mobo/processor from a p3 550 to an amd athalon 2400+ |
Nice choice on the processor 
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Gentoo...it's like wiping your ass with silk. Or sandpaper. |
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fieryred2k
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Joined: 23 Mar 2004
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| Posted: Tue May 11, 2004 3:16 am Post subject: |
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| ok next question... would it be easier to do a fresh install? or for example boot from the live cd, chroot in and compile everything anew? or will that be even possible with the -march cflag? |
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YopWongSapn
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Joined: 26 Jan 2004
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| Posted: Tue May 11, 2004 2:25 pm Post subject: |
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| fieryred2k wrote: | | ok next question... would it be easier to do a fresh install? or for example boot from the live cd, chroot in and compile everything anew? or will that be even possible with the -march cflag? |
Well, you could chroot from the livecd and "emerge -D world", which would be easier than starting from scratch. However, the safest thing to do would be to make a fresh installation. This will ensure that everything on the system was compiled correctly and may save you some major headaches down the road. Plus, it'll be an opportunity to try out the 2004.1 livecd 
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YopWongSapn
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Joined: 26 Jan 2004
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| Posted: Tue May 11, 2004 2:48 pm Post subject: |
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| fieryred2k wrote: | | or will that be even possible with the -march cflag? |
Changing the -march/mcpu flag will be fine. The one you don't want to change is CHOST, which it appears you will have to do. So, disregard my previous post
You will need to start your gentoo installation over.
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lbrtuk
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Joined: 08 May 2003
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| Posted: Tue May 11, 2004 4:15 pm Post subject: |
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NO!
You do not have to recompile.
The athlon supports all instructions that the pentium 3 does - it will understand all pentium 3 code. Of course recompiling will give you a speedup, but I suggest that rather than doing a complete wipe, you just change your cflags and everything you subsequently compile will be optimised to the new settings. This way, in a few moths you will probably have recompiled everything, having a fully optimised system.
Now where you run into problems is when you downgrade processors. Older processors do not always support the same instructions as newer ones, so they will not understand some of the asm instructions sent to them. But even then, nowadays that only applies to programs that have specially programmed SIMD instructions (most don't). Things like mplayer do. This would not be the case if gcc did autovectorisation (automatic generation of SIMD code even when not specially programmed), but it doesn't. So you're fine even then.
I suggest even though things should be fine, recompiling your kernel may be a good step.
This question has been answered many many times on these forums. A search would have helped you. |
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YopWongSapn
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Joined: 26 Jan 2004
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| Posted: Tue May 11, 2004 4:28 pm Post subject: |
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| lbrtuk wrote: | NO!
You do not have to recompile.
The athlon supports all instructions that the pentium 3 does - it will understand all pentium 3 code. Of course recompiling will give you a speedup |
Although this is true, lbrtuk didn't put the right amount of emphasis on the speed factor. I tried to cut corners a while back going from a pIII (700 I think) to athlon xp 1900+ and did exactly that...just changed the CFLAGS and figured everything would recompile. Of course, everything did recompile and everything was fine a few weeks down the road, running pIII code on my athlon was just aggravating. My system actually ran slower on the athlon than the pIII. If you want to save yourself the anguish of a sluggish system, I recommend a fresh install. Chrooting and recompiling everything would help, but in the long run it would be best to start over.
Plus, with the super-pimp speed of an athlon xp, it won't take long to get the system up and running again. 
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fieryred2k
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Joined: 23 Mar 2004
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| Posted: Tue May 11, 2004 4:29 pm Post subject: |
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| my chost is i686-pc-linux-gnu which is what I thought I'd have to leave it at. Reinstalling does seem to be the best idea, one last question then I'll stop pestering everyone can I install from the gentoo livecd, then copy over the world and system files and then do an emerge -D world and not have to re-select everything I have installed? |
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YopWongSapn
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Joined: 26 Jan 2004
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| Posted: Tue May 11, 2004 4:33 pm Post subject: |
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| fieryred2k wrote: | | can I install from the gentoo livecd, then copy over the world and system files and then do an emerge -D world and not have to re-select everything I have installed? |
I don't see a problem with that, as the world db is not architecture-specific. Same goes for most system files, but you'll want to be careful about which ones from the new install you overwrite....sometimes that can get messy. It wouldn't hurt to back up your /etc directory if you can spare the hdd space...then you'll be able to restore your settings for things like sshd, etc.
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lbrtuk
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| Posted: Tue May 11, 2004 4:46 pm Post subject: |
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I'm afraid to disagree, but I really wouldn't bother going through the reinstall rigamorole. I have helped about 4 people do this and I think
YopWongSapn's experiences must be an anomaly. Nobody else has had these problems at all.
But it's your decision. |
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fieryred2k
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Joined: 23 Mar 2004
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| Posted: Tue May 11, 2004 5:42 pm Post subject: |
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Well in addition to the new mobo/processor I'll be installing a seperate larger HD for gentoo, so it's either reinstall or copy over and have the possibility of there being problems because of how my entire distro is compiled... as well as I'm curious how fast gentoo would compile from step 1 on an athelon, so far I've compiled it on a p2 333 laptop, this p3 550 desktop, and soon to be athelon. guess I'm a complete nerd like the rest of you  thanks to you all for the help |
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Kernel & Hardware
