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[SOLVED]What Is Required (i.e.Recompilation?) If I Swap CPU?
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sk3l
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PostPosted: Thu Aug 01, 2013 11:51 am    Post subject: [SOLVED]What Is Required (i.e.Recompilation?) If I Swap CPU? Reply with quote

I currently roll with a i7-920 quad core. It's a great chip, but I found a steal of a bargain on eBay for an i7-970 hexacore that I couldn't pass up. The i7-970 is due to arrive any day, and after I swap it in, I'm wondering what I should do, if anything, in the way of recompiling my kernel (and any other installed software). I am using -march=native as my CFLAGS, so no chip specific options are explicitly enabled. My assumption is that everything will Just Work(tm) but that I ~may~ benefit from a recompile of kernel/world. I know I should adjust my -j and -load-average options now, as I will effectively go from 8 to 12 logical cores. Also interested in how this will impact my Windows guest in KVM, but that is another topic.

Last edited by sk3l on Thu Aug 01, 2013 7:46 pm; edited 1 time in total
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666threesixes666
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PostPosted: Thu Aug 01, 2013 1:38 pm    Post subject: Reply with quote

heh, NOTHING. i switched from a sempron x1 to change motherboard bios to a phenom 9950 x4 with nothing changed.
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roarinelk
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PostPosted: Thu Aug 01, 2013 2:02 pm    Post subject: Reply with quote

UPgrading should never be a problem. Worst case your environment won't use any of the newer CPU features.
DOWNgrading and changing CPU vendor is another story and might get you "illegal instruction" errors for example.
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Mac Tzu
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PostPosted: Thu Aug 01, 2013 2:53 pm    Post subject: Reply with quote

roarinelk wrote:
UPgrading should never be a problem. Worst case your environment won't use any of the newer CPU features.
DOWNgrading and changing CPU vendor is another story and might get you "illegal instruction" errors for example.


Sk3l,

As abundantly state the short answer is not much. Also it might be hard to tell CPU options have might have changed because you used native and haven't explicitly directly GCC . Depending on the generation of you have new AVX enabled on new CPU. (http://en.wikipedia.org/wiki/Advanced_Vector_Extensions). Which I call in my make.conf with march='icore7-avx'.

While it is unnecessary you could try out your new beastie with a emerge -e @system @world and ask genlop how much more awesome your new CPU is.

I pretty sure genlop will say you machine is pretty awesome ;-)
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sk3l
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PostPosted: Thu Aug 01, 2013 7:36 pm    Post subject: Reply with quote

Mac Tzu wrote:
roarinelk wrote:
UPgrading should never be a problem. Worst case your environment won't use any of the newer CPU features.
DOWNgrading and changing CPU vendor is another story and might get you "illegal instruction" errors for example.


Sk3l,

As abundantly state the short answer is not much. Also it might be hard to tell CPU options have might have changed because you used native and haven't explicitly directly GCC . Depending on the generation of you have new AVX enabled on new CPU. (http://en.wikipedia.org/wiki/Advanced_Vector_Extensions). Which I call in my make.conf with march='icore7-avx'.

While it is unnecessary you could try out your new beastie with a emerge -e @system @world and ask genlop how much more awesome your new CPU is.

I pretty sure genlop will say you machine is pretty awesome ;-)


Looks like AVX first appeared in Sandy Bridge architecture, of which the i7-970 (AFAIK) is not based on.
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sk3l
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PostPosted: Thu Aug 01, 2013 7:44 pm    Post subject: Reply with quote

Thanks everyone, seems like everything should be fine without a recompile, as I suspected. Now that I look at the chip architectures side by side, 920 (Nehalem) against 970 (Westmere), the only real difference I see is enhanced support for AES encryption (AES-NI) built into the 970's instruction set. Apparently besides shoving 2 more cores onto the die, there wasn't much progression between the two architectures.
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Ant P.
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PostPosted: Sat Aug 03, 2013 3:34 pm    Post subject: Reply with quote

roarinelk wrote:
UPgrading should never be a problem. Worst case your environment won't use any of the newer CPU features.
DOWNgrading and changing CPU vendor is another story and might get you "illegal instruction" errors for example.

The one exception to this is going from an AMD Phenom to a Bulldozer — they removed the 3DNow instruction sets between those.
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PatomaS
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PostPosted: Fri Aug 30, 2013 2:57 am    Post subject: Reply with quote

Hi

Although it shouldn't be a problem, sometimes there may be a lot of them

Recently I switched from an Intel I5-2500K, to an Intel I5-3330, and I'm still trying to get my system to work.

The easy guess is that the virtualization options are affecting, but in this case, all those options are off, in the UEFI and in the kernel.

So, I'd say, always keep the original at hand or at least don't do changes if you are short on time or close to any kind of deadline.

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