Re: [gentoo-user] common flags for 2 cpu?

[Jorge Almeida]

On Fri, Aug 17, 2012 at 2:53 PM, Florian Philipp <lists@×××××××××××.net> wrote:
> Am 17.08.2012 10:58, schrieb Jorge Almeida:
>>
>> 1) Is this strategy right? If so, any other flags to add? (or any
>> flags to remove from the list?)
>>
>> 2) The --param flags are the ones of the computer that will do the
>> compiling. I'm guessing the produced binaries are compatible with cpu
>> with different --param flags. Is this right?
>>
>> TIA
>>
>> Jorge Almeida
>>
>
> 1) Yes. But as you can see, -march=prescott is basically a subset of
> atom. In fact, before there was a -march=atom option, prescott was the
> best flag for atoms. I think you can avoid some hassle by simply
> enabling "-march=prescott --param l1-cache-line-size=64 --param
> l2-cache-size=512".
>
> 2) Yes, the param flags do not affect compatibility. Using the lower
> value will probably be better but this is just an educated guess.
>

What about:

CFLAGS="-O2 -pipe -fomit-frame-pointer -march=prescott -mtune=atom --param
l1-cache-size=16 --param l1-cache-line-size=64 --param l2-cache-size=1024"

If prescott were exactly a subset of atom, this would yield the best of both
worlds. Can it still be safe?

I read in http://forums.gentoo.org/viewtopic-t-895104.html :
atom
Intel Atom CPU with 64-bit extensions, MMX, SSE, SSE2, SSE3 and SSSE3
instruction set support.

Does this mean that these flags are pulled by -mtune=atom, or do we need to
ask for them explicitly? The WiKi shows how to find which flags are pulled by
-march=native, but not the other cases.

Thanks

Jorge Almeida