Re: [gentoo-user] CPU upgrade and LVM questions.

[Alexander Puchmayr <alexander.puchmayr@linznet.at>]

Am Donnerstag, 6. Dezember 2018, 10:27:31 CET schrieb Dale:
> Howdy,
> 
> I mentioned in other threads that I'm doing some upgrades to my system. 
> My first question is about a CPU upgrade.  I currently have this for my
> CPU, from cpuinfo:
> 
> AMD Phenom(tm) II X4 955 Processor
> 
> I've bought but not yet installed a FX-8350 CPU.  I have this in my
> make.conf file:
> 
> CFLAGS="-march=native -O2 -pipe"

Compiling the whole system with -march=native might lead to troubles, 
especially when doing a CPU change. This option means that gcc is determining 
the type of CPU automatically and adjusts the instruction set used to exactly 
this CPU. Although, in your case, it is highly likely that your new CPU 
understands all commands from the old, but I wouldn't bet on it. Its possible 
that your existing software encounters problems like "illegal instruction" or 
the like. Very bad if your compiler crashes after CPU replacement, then you 
cannot emerge anything. I highly recommend using CFLAGS="-O2 -pipe" and 
nothing more, the performance difference is, if measurable at all, negligible. 

> USE_CPU="fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov
> pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt
> pdpe1gb rdtscp lm 3dnowext 3dnow constant_tsc rep_good nopl nonstop_tsc
> extd_apicid pni monitor cx16 popcnt lahf_lm cmp_legacy svm extapic
> cr8_legacy abm sse4a misalignsse 3dnowprefetch osvw ibs skinit wdt
> nodeid_msr hw_pstate npt lbrv svm_lock nrip_save"
> 
As someone else in this thread already mentioned, USE_CPU is not used. What 
you're looking for is CPU_FLAGS_X86=..., which defines what cpu-specific options 
will be enabled for packages supporting it and where it makes sense. See 
package cpuid2cpuflags for details.

Regards
	Alex