Re: [gentoo-user] Re: -march=auto

Re: [gentoo-user] Re: -march=auto

[maxim wexler]

--- On Thu, 5/21/09, Alex Schuster <wonko@wonkology.org> wrote:

> From: Alex Schuster <wonko@wonkology.org>
> Subject: [gentoo-user] Re: -march=auto
> To: gentoo-user@lists.gentoo.org
> Received: Thursday, May 21, 2009, 12:30 PM
> I just wrote:
> 
> > > Could also perhaps try -march=auto if you're
> using a version of GCC
> > > that supports it.
> 
> Oh, it's -march=native.
> 
> > BTW, is there a possibility to let gcc tell what flags
> it will actually
> > use with -march=auto?
> 
> Paul Hartman just posted a link to a script that seems to
> do what I was 
> looking for in the "[OT]eee 900a intel atom is what
> processor family?" 
> thread: <http://www.pixelbeat.org/scripts/gcccpuopt>
> 
> But it suggests using -march=k8 - isn't that a 64-bit-only
> thing? I'm not 

For an 900A w/intel Atom?

This is what I get:

Warning: Your compiler supports the -march=native option which you may prefer
Warning: Newer versions of GCC better support your CPU with -march=atom
-march=core2 -mtune=pentium -mfpmath=sse.

Now I'm confused. It says *my* compiler supports -march=native. Then it says "Newer versions". Isn't v4.3.2 new? It was from a new pkg about a month ago. Is it giving me a choice here? Can I really declare two -march variables? What about mtune and mfpath, are they meant to be "instead of" or "in addition to"? What goes in the kernel config? What in /etc/paludis/bashrc?

Maxim




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[gentoo-user] Re: -march=auto

[ABCD]

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Hash: SHA1

maxim wexler wrote:
> 
> For an 900A w/intel Atom?
> 
> This is what I get:
> 
> Warning: Your compiler supports the -march=native option which you
> may prefer

If you use this, then you 1) must be using >=sys-devel/gcc-4.2, and 2)
will always have the "best" optimization for your machine, so far as the
version of gcc you are using understands.

> Warning: Newer versions of GCC better support your CPU with -march=atom

In order to use this, you will need gcc-4.5, which hasn't been released yet.

> -march=core2 -mtune=pentium -mfpmath=sse.

This is the recommendation that the script actually made - it suggests
to use all of these.

> Now I'm confused. It says *my* compiler supports -march=native. Then
> it says "Newer versions". Isn't v4.3.2 new? It was from a new pkg about
> a month ago. Is it giving me a choice here? Can I really declare two
> -march variables? What about mtune and mfpath, are they meant to be
> "instead of" or "in addition to"? What goes in the kernel config? What
> in /etc/paludis/bashrc?

The newest version of gcc out right now is 4.4.0 (currently in
package.mask).  I would suggest setting CFLAGS="-O2 -march=native -pipe"
and CXXFLAGS="-O2 -march=native -pipe" in /etc/paludis/bashrc (assuming
that that is the proper location for those variables).

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Re: [gentoo-user] Re: -march=auto

[Alex Schuster]

maxim wexler writes:

> --- On Thu, 5/21/09, Alex Schuster <wonko@wonkology.org> wrote:

> > But it suggests using -march=k8 - isn't that a 64-bit-only
> > thing? I'm not
>
> For an 900A w/intel Atom?

No, I have an AMD Athlon(tm) Dual Core Processor 4850e.

> This is what I get:
>
> Warning: Your compiler supports the -march=native option which you may
> prefer Warning: Newer versions of GCC better support your CPU with
> -march=atom -march=core2 -mtune=pentium -mfpmath=sse.
>
> Now I'm confused. It says *my* compiler supports -march=native. Then it
> says "Newer versions". Isn't v4.3.2 new? It was from a new pkg about a
> month ago. Is it giving me a choice here? Can I really declare two -march
> variables? What about mtune and mfpath, are they meant to be "instead of"
> or "in addition to"?

I'm also confused. Multiple -march options make no sense I believe, as does 
specifying both -march and -mtune, as -mtune is implied by -march. And the 
docs say in the section about
-mfpmath=sse:

        For the i386 compiler, you need to use `-march=CPU-TYPE',
        `-msse' or `-msse2' switches to enable SSE extensions and
        make this option effective.  For the x86-64 compiler, these
        extensions are enabled by default.

So it seems to me that -mfpmath does not need to be set.

Well, I'd just use -march=native, unless when using distcc. If so, Daniel's 
tip about 'gcc -Q --help=target -march=native' will give you the exact 
options to use.
 
	Wonko

Re: [gentoo-user] Re: -march=auto

[maxim wexler]

[-- Attachment #1: Type: text/plain, Size: 476 bytes --]

> If so, Daniel's 
> tip about 'gcc -Q --help=target -march=native' will give
> you the exact 
> options to use.
>  
>     Wonko
> 
>

See attachment please. Some stuff is enabled, some disabled, some blank. And -march=prescott !?

Maxim


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[-- Attachment #2: gcc-Q --]
[-- Type: application/octet-stream, Size: 2767 bytes --]

The following options are target specific:
  -m128bit-long-double        		[disabled]
  -m32                        		[enabled]
  -m3dnow                     		[disabled]
  -m3dnowa                    		[disabled]
  -m64                        		[disabled]
  -m80387                     		[enabled]
  -m96bit-long-double         		[enabled]
  -mabm                       		[disabled]
  -maccumulate-outgoing-args  		[disabled]
  -malign-double              		[disabled]
  -malign-functions=          		
  -malign-jumps=              		
  -malign-loops=              		
  -malign-stringops           		[enabled]
  -march=                     		prescott
  -masm=                      		
  -mbranch-cost=              		
  -mcld                       		[disabled]
  -mcmodel=                   		
  -mcx16                      		[disabled]
  -mfancy-math-387            		[enabled]
  -mfp-ret-in-387             		[enabled]
  -mfpmath=                   		
  -mfused-madd                		[enabled]
  -mglibc                     		[enabled]
  -mhard-float                		[enabled]
  -mieee-fp                   		[enabled]
  -minline-all-stringops      		[disabled]
  -minline-stringops-dynamically 	[disabled]
  -mintel-syntax              		[disabled]
  -mlarge-data-threshold=     		
  -mmmx                       		[disabled]
  -mms-bitfields              		[disabled]
  -mno-align-stringops        		[disabled]
  -mno-fancy-math-387         		[disabled]
  -mno-push-args              		[disabled]
  -mno-red-zone               		[disabled]
  -mno-sse4                   		[enabled]
  -momit-leaf-frame-pointer   		[disabled]
  -mpc                        		
  -mpopcnt                    		[disabled]
  -mpreferred-stack-boundary= 		
  -mpush-args                 		[enabled]
  -mrecip                     		[disabled]
  -mred-zone                  		[enabled]
  -mregparm=                  		
  -mrtd                       		[disabled]
  -msahf                      		[enabled]
  -msoft-float                		[disabled]
  -msse                       		[disabled]
  -msse2                      		[disabled]
  -msse3                      		[disabled]
  -msse4                      		[disabled]
  -msse4.1                    		[disabled]
  -msse4.2                    		[disabled]
  -msse4a                     		[disabled]
  -msse5                      		[disabled]
  -msseregparm                		[disabled]
  -mssse3                     		[disabled]
  -mstack-arg-probe           		[disabled]
  -mstackrealign              		[disabled]
  -mstringop-strategy=        		
  -mtls-dialect=              		
  -mtls-direct-seg-refs       		[enabled]
  -mtune=                     		generic
  -muclibc                    		[disabled]
  -mveclibabi=                		

Re: [gentoo-user] Re: -march=auto

[Alex Schuster]

maxim wexler writes:

> > If so, Daniel's tip about 'gcc -Q --help=target -march=native' will give
> > you the exact options to use.

> See attachment please. Some stuff is enabled, some disabled, some blank.

Try this:
gcc -Q --help=target -march=native > /tmp/gccoptions.native
gcc -Q --help=target               > /tmp/gccoptions.plain
diff /tmp/gccoptions.*

This will show the things that specifying -march=native turns on. Put this 
in your CFLAGS, unless you use -march=native.

> And -march=prescott !?

Why not? Seems gcc 4.3 does not have the -march=atom optimization yet. It's 
also suggested here:
http://en.gentoo-wiki.com/wiki/Safe_Cflags/Intel#Atom

	Wonko

[gentoo-user] [OT]eee 900a intel atom is what processor family?

[maxim wexler]

Hi group,

Going through my kernel config I see CONFIG_M686 "Pentium Pro". That can't be right. 

But there is nothing for Intel Atom, the 900A's processor. Is it CONFIG_M586?
Is CONFIG_M386 my best choice, the default?

BTW /etc/paludis/bashrc lists:

CFLAGS="-02 -march=i686 -pipe". Is that supposed to reflect the proper kernel config. Is it "Pentium Pro" afterall?

Maxim.



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Re: [gentoo-user] [OT]eee 900a intel atom is what processor family?

[Paul Hartman]

On Thu, May 21, 2009 at 2:46 AM, Neil Bothwick <neil@digimed.co.uk> wrote:
> On Wed, 20 May 2009 19:52:44 -0700 (PDT), maxim wexler wrote:
>
>> Going through my kernel config I see CONFIG_M686 "Pentium Pro". That
>> can't be right.
>>
>> But there is nothing for Intel Atom, the 900A's processor. Is it
>> CONFIG_M586? Is CONFIG_M386 my best choice, the default?
>
> AFAIK, CONFIG_MCORE2 is the correct choice.
>
>> BTW /etc/paludis/bashrc lists:
>>
>> CFLAGS="-02 -march=i686 -pipe". Is that supposed to reflect the proper
>> kernel config. Is it "Pentium Pro" afterall?
>
> And -march=prescott
>
> The more generic choices you have will work, but be slightly less
> optimised.

Could also perhaps try -march=auto if you're using a version of GCC
that supports it.

-march=auto (was: Re: [gentoo-user] [OT]eee 900a intel atom is what processor family?)

[Alex Schuster]

Paul Hartman writes:

> Could also perhaps try -march=auto if you're using a version of GCC
> that supports it.

BTW, is there a possibility to let gcc tell what flags it will actually use 
with -march=auto?
Oh, and is your gcc man page empty, too? 'info gcc' works, though. But I did 
not find what I was looking for.

	Wonko

[gentoo-user] Re: -march=auto

[Alex Schuster]

I just wrote:

> > Could also perhaps try -march=auto if you're using a version of GCC
> > that supports it.

Oh, it's -march=native.

> BTW, is there a possibility to let gcc tell what flags it will actually
> use with -march=auto?

Paul Hartman just posted a link to a script that seems to do what I was 
looking for in the "[OT]eee 900a intel atom is what processor family?" 
thread: <http://www.pixelbeat.org/scripts/gcccpuopt>

But it suggests using -march=k8 - isn't that a 64-bit-only thing? I'm not 
compiling for AMD64, I'm still using 32-bit mode. So I have -march=athlon-xp 
in my CFLAGS for my AMD Athlon(tm) Dual Core Processor 4850e CPU.

	Wonko

Re: [gentoo-user] Re: -march=auto

[Paul Hartman]

On Thu, May 21, 2009 at 2:30 PM, Alex Schuster <wonko@wonkology.org> wrote:
> Paul Hartman just posted a link to a script that seems to do what I was
> looking for in the "[OT]eee 900a intel atom is what processor family?"
> thread: <http://www.pixelbeat.org/scripts/gcccpuopt>
>
> But it suggests using -march=k8 - isn't that a 64-bit-only thing? I'm not
> compiling for AMD64, I'm still using 32-bit mode. So I have -march=athlon-xp
> in my CFLAGS for my AMD Athlon(tm) Dual Core Processor 4850e CPU.

Hi,

That script says it is specifically for 32-bit only, so I think you
should be good.

According to:
http://gcc.gnu.org/onlinedocs/gcc-4.3.3/gcc/i386-and-x86_002d64-Options.html

It looks like that CPU type supports the amd64 instruction set but I
don't think itt necessarily means you are using it in 64-bit mode. I
think it would just simply not work at all if it's not valid for
32-bit mode.

Re: [gentoo-user] Re: -march=auto

[Peter Humphrey]

On Thursday 21 May 2009 20:30:19 Alex Schuster wrote:

> Paul Hartman just posted a link to a script that seems to do what I was
> looking for in the "[OT]eee 900a intel atom is what processor family?"
> thread: <http://www.pixelbeat.org/scripts/gcccpuopt>

It's the same thread as your own message is in. Changing the subject does 
not remove references from headers, nor should it. In other words, if you 
want to start a new thread, click "new", not "reply".

</soapbox>

-- 
Rgds
Peter

Re: [gentoo-user] Re: -march=auto

[Alex Schuster]

Peter Humphrey writes:

> On Thursday 21 May 2009 20:30:19 Alex Schuster wrote:
> > Paul Hartman just posted a link to a script that seems to do what I was
> > looking for in the "[OT]eee 900a intel atom is what processor family?"
> > thread: <http://www.pixelbeat.org/scripts/gcccpuopt>
>
> It's the same thread as your own message is in. Changing the subject does
> not remove references from headers, nor should it. In other words, if you
> want to start a new thread, click "new", not "reply".

I wanted to keep the thread, but change the topic accordingly. I just did 
not check the original topic, so I overlooked the posting I mentioned was 
supposed to be in the same thread - that's a little silly of me, actually :) 
It shows up in a different thread, though, because the references were lost. 
looks like Maxim's YahooMailWebService always drops them.

	Wonko

Re: -march=auto (was: Re: [gentoo-user] [OT]eee 900a intel atom is what processor family?)

[Daniel Iliev]

On Thu, 21 May 2009 21:08:59 +0200
Alex Schuster <wonko@wonkology.org> wrote:

> Paul Hartman writes:
> 
> > Could also perhaps try -march=auto if you're using a version of GCC
> > that supports it.
> 
> BTW, is there a possibility to let gcc tell what flags it will
> actually use with -march=auto?



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


-- 
Best regards,
Daniel

[gentoo-user] Re: -march=auto

[Alex Schuster]

Daniel Iliev writes:

> Alex Schuster <wonko@wonkology.org> wrote:

> > BTW, is there a possibility to let gcc tell what flags it will
> > actually use with -march=auto?
>
> gcc -Q --help=target  -march=native

Cool, thanks!

	Wonko