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On 06/12/2018 11:27, Dale wrote: |
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> |
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> I've bought but not yet installed a FX-8350 CPU. I have this in my |
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> make.conf file: |
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> |
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> CFLAGS="-march=native -O2 -pipe" |
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> USE_CPU=" |
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USE_CPU does not do anything, AFAICT. CPU features are specified in |
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CPU_FLAGS_X86. You can get appropriate flags using the |
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app-portage/cpuid2cpuflags tool. For example, here: |
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$ cpuid2cpuflags |
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CPU_FLAGS_X86: aes avx mmx mmxext pclmul popcnt sse sse2 sse3 sse4_1 |
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sse4_2 ssse3 |
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So in my make.conf, I use: |
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CPU_FLAGS_X86="aes avx mmx mmxext pclmul popcnt sse sse2 sse3 sse4_1 |
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sse4_2 ssse3" |
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> Those were put there ages ago, likely when I built and installed Gentoo |
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> on this rig. Do I need to change those to something that is compatible |
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> with both CPUs and then change to the new CPU after it is installed? Or |
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> will the new CPU be close enough that it won't matter? Right now, I |
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> don't know for sure what the new CPU supports or doesn't. |
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Just install the new CPU and run cpuid2cpuflags to see what to put in |
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CPU_FLAGS_X86. You can delete USE_CPU as that doesn't seem to be used |
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for anything. |
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> While at it, going from a 4 core CPU at 3.2GHz to a 8 core CPU at |
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> 4.0/4.2GHz, just how much increase can I expect? Will it double and |
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> that's about it or will it be more than that? |
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You won't get anything close to double the speed. The extra cores will |
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mostly go unused, unless you use applications that make use of them. |
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You will still get a speed up due to the newer CPU architecture and the |
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higher frequency. |
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> Also, since it has two |
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> speeds, will it run at the slower or faster one? Will it depend on |
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> load? I've never had a CPU with two clock speeds like this before. |
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The two speeds specify the lower and upper speeds, depending on how many |
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CPU cores are currently being under load, and also how much load there |
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is. You don't have to worry about it though. It's all automatic. When |
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you're not running anything that stressed the CPU, clock speeds are |
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actually lower than 4GHz (some CPUs can clock down to 1GHz or so when |
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they're idle and not doing anything.) Once something CPU-heavy runs, it |
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will clock up to 4.2GHz. If you run something that stresses all CPU |
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cores, then it will go to 4.0GHz to avoid overheating. |
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But again, all this is automatic. |
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