switch processors in system

[luap]

hello,
i currently am using an athlon tb 850, and set cflags to optimize for
this processor. i inherited an athlon xp 1600, and i want to replace the
athlon 850.
i am a bit hazy on the interaction of the use flags/cflags and swapping
processors- do i need to start from the beginning-reinstall?
or could i do something like this-
--set cflags to generic i386, recompile kernel
-- swap out processors
-- set cflags to athlon xp recompile kernel

or is their a howto or thread covering this process? thanks

[mpsii]

You should not have to start from scratch. It might be a good idea to recompile your kernel for i586 and set it as the backup kernel, in case your current one does not work when you install the new proc.

With your CFLAGS... If you had it set to -mcpu=athlon or similar, you should be okay. However, if you set it to -march=athlon or similar, you will have problems.

In the case of the -march setting, I would suggest changing it to -mcpu and emerge --deep world, recompile your kernel as mentioned above, and then install your new processor. At that point, recompile your kernel to take advantage of the XP and set your CFLAGS to -mcpu=athlon-xp. From there, just continue to update your software as you would normally. In a short amount of time, the system will be tuned naturally to the new settings. Otherwise, you could run emerge --deep world again, but I think that would be a time spender.

Just my .02
_________________
-----------------------------------------
Michael

[nerdbert]

I think you should swap your cpus prior to any time consuming actions

haven't tried it myself, but there is a good chance that your new XP will understand your Athlon binaries (mpsii: are you sure that a XP won't work with mach=athlon?).

you will still have to recompile everything (I'm assuming you want bleeding-edge performance), but you only have to do it once.

[mpsii]

[luap]

hello
thanks all for the help and suggestions.
please excuse my linux maroon-ness, i just want to be sure i
understand-
is it the emerge world process that recompiles software to cflags settings?
cause i guess i was stupidly thinking recompile kernel.....
but i wont need to recompile the kernel?
bless you all for your patience!

[guero61]

Well... I don't think you need to recompile world (emerge -e --deep world) unless you absolutely insist on every package being minutely optimized for your new proc. Same with the kernel -- it should work with your new kernel, but you can recompile it to be athlon-xp instead of athlon.

I say replace the processor outright and see if it'll boot up. If it does, you're in luck -- just let the older software be phased out slowly. If it totally fubars, the worst you'd have to do is reboot into the install cd, chroot, and recompile your kernel.

[lbrtuk]

It'll work fine.

I recently did something similar, but far more drastic.

You've got to think of it on the assmebly level, y'see.

I went from a k6-2 350 to a dual pII 400 a couple of months ago.

Now, in that situation, I had to think whether there were any instructions the k6-2 had that the pII doesn't. There aren't. (EXCEPT 3dnow, but since i was using gcc 2.95.3, the compiler didnt use those instructions)

There were a couple of applications like mplayer that i had to recompile because they had put in their own 3dnow optimised assembly.

It is still a good idea to do an i586 kernel though.

There are not any instructions for an athlon that an XP doesn't implement. So it should all work.