[gentoo-user] -march=native

[gentoo-user] -march=native

[Hasan SAHIN]

Hello all,

I am using Athlon64 X2 processor with the
CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.

Can I use the -march=native option instead of that?

P.S. : I am using x86 stable box.

Regards,
Hasan.

Re: [gentoo-user] -march=native

[Bill Longman]

On 06/29/2010 05:54 PM, Hasan SAHIN wrote:
> Hello all,
> 
> I am using Athlon64 X2 processor with the
> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
> 
> Can I use the -march=native option instead of that?
> 
> P.S. : I am using x86 stable box.

Depends more on the version of gcc you're using. And you can also add
-msse on the X2. Supposedly there's a -march=k8-sse but in my experience
it was not good. Others may have different experience.

Re: [gentoo-user] -march=native

[Alex Schuster]

Hasan SAHIN writes:

> I am using Athlon64 X2 processor with the
> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
> 
> Can I use the -march=native option instead of that?

Sure, as long as you are not using distcc, in which case the distcc 
servers would compile according to _their_ native option.

	Wonko

Re: [gentoo-user] -march=native

[Bill Longman]

On 06/29/2010 05:54 PM, Hasan SAHIN wrote:
> Hello all,
> 
> I am using Athlon64 X2 processor with the
> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
> 
> Can I use the -march=native option instead of that?

Sorry, Hasan, I dropped my "3"s.

-msse3 and -march=k8-sse3

Re: [gentoo-user] -march=native

[Hasan SAHIN]

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29-06-2010 22:03, Bill Longman yazmış:
> On 06/29/2010 05:54 PM, Hasan SAHIN wrote:
>    
>> Hello all,
>>
>> I am using Athlon64 X2 processor with the
>> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
>>
>> Can I use the -march=native option instead of that?
>>      
> Sorry, Hasan, I dropped my "3"s.
>
> -msse3 and -march=k8-sse3
>    
Hi Bill,

I have read the safe flags document and it says that :

/GCC 4.2 introduces a new -march option, -march=*native*, which 
automatically detects the features your CPU supports and sets the 
options appropriately. If you have an Intel or AMD CPU and are using 
 >=sys-devel/gcc-4.2.3, using -march=native is recommended. Do *not* use 
-march=native if you use distcc on nodes with different architectures as 
this may produce unusable code. /

which I understood, I can use the -march=native option instead of

CFLAGS="-march=k8-msse3 -O2 -pipe -fomit-frame-pointer"

is it true?

Regards,
Hasan.


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Re: [gentoo-user] -march=native

[Bill Longman]

On 06/29/2010 06:08 PM, Hasan SAHIN wrote:
> I have read the safe flags document and it says that :
> 
> /GCC 4.2 introduces a new -march option, -march=*native*, which
> automatically detects the features your CPU supports and sets the
> options appropriately. If you have an Intel or AMD CPU and are using
>>=sys-devel/gcc-4.2.3, using -march=native is recommended. Do *not* use
> -march=native if you use distcc on nodes with different architectures as
> this may produce unusable code. /
> 
> which I understood, I can use the -march=native option instead of
> 
> CFLAGS="-march=k8-msse3 -O2 -pipe -fomit-frame-pointer"
> 
> is it true?

Yes, -march=native is a good, simple way to optimize your compiles.
Here's what you should use on your Athlon64 X2, then:

  CFLAGS="-march=native -O2 -pipe"

Re: [gentoo-user] -march=native

[Paul Hartman]

2010/6/29 Hasan SAHIN <hasan.sahin@gmx.com>:
> Hello all,
>
> I am using Athlon64 X2 processor with the
> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
>
> Can I use the -march=native option instead of that?

You can see which options -march=native would use by running this command:

gcc -Q --help=target  -march=native

(thanks to Daniel Iliev for the tip)

Re: [gentoo-user] -march=native

[Beau Henderson]

On 06/30/10 08:07, Paul Hartman wrote:
> 2010/6/29 Hasan SAHIN<hasan.sahin@gmx.com>:
>> Hello all,
>>
>> I am using Athlon64 X2 processor with the
>> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
>>
>> Can I use the -march=native option instead of that?
>
> You can see which options -march=native would use by running this command:
>
> gcc -Q --help=target  -march=native
>
> (thanks to Daniel Iliev for the tip)
>

Perhaps I'm missing something but running the above gives me the impression that -march=native 
actually only configures the bare minimal install. I'm not seeing -mmmx or -msse3 enabled on my 
k8-sse3 for instance ( amongst much else ).

Re: [gentoo-user] -march=native

[Albert Hopkins]

On Wed, 2010-06-30 at 11:09 +1000, Beau Henderson wrote:
> On 06/30/10 08:07, Paul Hartman wrote:
[...]
> > You can see which options -march=native would use by running this command:
> >
> > gcc -Q --help=target  -march=native
> >
> > (thanks to Daniel Iliev for the tip)
> >
> 
> Perhaps I'm missing something but running the above gives me the impression that -march=native 
> actually only configures the bare minimal install. I'm not seeing -mmmx or -msse3 enabled on my 
> k8-sse3 for instance ( amongst much else ).
> 

-march sometimes implies a some things.  E.g., anything above a pentium2
implies MMX.  My hunch is that k8-sse3 implies... sse3.

Re: [gentoo-user] -march=native

[Paul Hartman]

On Tue, Jun 29, 2010 at 8:54 PM, Albert Hopkins <marduk@letterboxes.org> wrote:
> On Wed, 2010-06-30 at 11:09 +1000, Beau Henderson wrote:
>> On 06/30/10 08:07, Paul Hartman wrote:
> [...]
>> > You can see which options -march=native would use by running this command:
>> >
>> > gcc -Q --help=target  -march=native
>> >
>> > (thanks to Daniel Iliev for the tip)
>> >
>>
>> Perhaps I'm missing something but running the above gives me the impression that -march=native
>> actually only configures the bare minimal install. I'm not seeing -mmmx or -msse3 enabled on my
>> k8-sse3 for instance ( amongst much else ).
>>
>
> -march sometimes implies a some things.  E.g., anything above a pentium2
> implies MMX.  My hunch is that k8-sse3 implies... sse3.

See this page of the GCC documentation for some info about what is
enabled in the different arches:

http://gcc.gnu.org/onlinedocs/gcc-4.4.3/gcc/i386-and-x86_002d64-Options.html

Re: [gentoo-user] -march=native

[Paul Hartman]

On Tue, Jun 29, 2010 at 8:09 PM, Beau Henderson <beau@thehenderson.com> wrote:
> On 06/30/10 08:07, Paul Hartman wrote:
>>
>> 2010/6/29 Hasan SAHIN<hasan.sahin@gmx.com>:
>>>
>>> Hello all,
>>>
>>> I am using Athlon64 X2 processor with the
>>> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
>>>
>>> Can I use the -march=native option instead of that?
>>
>> You can see which options -march=native would use by running this command:
>>
>> gcc -Q --help=target  -march=native
>>
>> (thanks to Daniel Iliev for the tip)
>>
>
> Perhaps I'm missing something but running the above gives me the impression
> that -march=native actually only configures the bare minimal install. I'm
> not seeing -mmmx or -msse3 enabled on my k8-sse3 for instance ( amongst much
> else ).

What -march setting is it showing in that output? The MMX (etc) may be
enabled implicitly instead of explicitly.

It's also possible that the CPU detection is failing to identify your
CPU. In that case you could probably file a bug report about it.

Re: [gentoo-user] -march=native

[Beau Henderson]

On 07/01/10 00:30, Paul Hartman wrote:
> On Tue, Jun 29, 2010 at 8:09 PM, Beau Henderson<beau@thehenderson.com>  wrote:
>> On 06/30/10 08:07, Paul Hartman wrote:
>>>
>>> 2010/6/29 Hasan SAHIN<hasan.sahin@gmx.com>:
>>>>
>>>> Hello all,
>>>>
>>>> I am using Athlon64 X2 processor with the
>>>> CFLAGS="-march=k8 -O2 -pipe -fomit-frame-pointer" option.
>>>>
>>>> Can I use the -march=native option instead of that?
>>>
>>> You can see which options -march=native would use by running this command:
>>>
>>> gcc -Q --help=target  -march=native
>>>
>>> (thanks to Daniel Iliev for the tip)
>>>
>>
>> Perhaps I'm missing something but running the above gives me the impression
>> that -march=native actually only configures the bare minimal install. I'm
>> not seeing -mmmx or -msse3 enabled on my k8-sse3 for instance ( amongst much
>> else ).
>
> What -march setting is it showing in that output? The MMX (etc) may be
> enabled implicitly instead of explicitly.
>
> It's also possible that the CPU detection is failing to identify your
> CPU. In that case you could probably file a bug report about it.
>

The correct -march is being displayed, I just can't make sense of the options showing as [disabled]. 
While the option may be implied by the -march settings, it just makes sense to me that the option 
should show as enabled. Indeed, with my core2 machine the majority of the options do display as 
enable as expected, just not with my k8-see3 @native.

I wonder if perhaps it might be possible to compile an application that uses all these functions and 
then assess ( somehow ) the binaries afterwards to see if they were compiled in and working correctly ?

Here's what I'm seeing on my k8-sse3: http://pastebin.com/PfMiTnx5

And my core2: http://pastebin.com/7WerGwkX

Re: [gentoo-user] -march=native

[James Cloos]

>>>>> "BH" == Beau Henderson <beau@thehenderson.com> writes:

BH> The correct -march is being displayed, I just can't make sense of the
BH> options showing as [disabled]. While the option may be implied by the
BH> -march settings, it just makes sense to me that the option should show
BH> as enabled. Indeed, with my core2 machine the majority of the options
BH> do display as enable as expected, just not with my k8-see3 @native.

FWIW, a tests on -march=amdfam10 on both gentoo and debian also show odd
enabled/disabled results, as do debian k8-sse3 and core2 boxen.  The
fedora core2 box I have access to, however, shows reasonable enableds.

Odd.

-JimC
-- 
James Cloos <cloos@jhcloos.com>         OpenPGP: 1024D/ED7DAEA6