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c.f. bug 424647
List Archive: gentoo-amd64
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To: gentoo-amd64@g.o
From: DJ Cozatt <ygdrasil@...>
Subject: Re: Digest of gentoo-amd64@g.o issue 367 (13009-13035)
Date: Fri, 08 Jul 2011 16:46:38 -0400
On Tue, 2011-07-05 at 13:02 +0000, gentoo-amd64+help@g.o
wrote:
>         On Thu, 30 Jun 2011 21:36:38 -0700
>         Mark Knecht <markknecht@...> wrote:
>         
>         > 
>         > I think it's completely appropriate for this list. This
>         distro expects
>         > that we put CFLAG options in make.conf so I need to hear
>         about this
>         > stuff even if I don't have to background to completely
>         understand
>         > what's really causing the problem.
>         > 
>         
>         In this case, or in the case of any program where
>         "-fno-strict-aliasing"
>         could make a difference, the maintainer of the program would
>         include
>         the option in the ebuild.  The user would not have to worry
>         too much
>         about it.
>         
>         But yes, it is always good to know about the compiler flags.
>         
>         To see exactly what compile flags are being used in your
>         programs, here
>         is a neat method I picked up from somewhere.  Just open a
>         terminal and
>         enter the following command:
>         
>         echo 'int main(){return 0;}' > test.c && gcc -v -Q $CFLAGS
>         test.c -o test && rm test.c test
>         
>         In place of $CFLAGS just substitute any option of interest.
>         There will
>         be a flood of output, but just scroll back a few lines to find
>         the "options
>         passed:" and "options enabled:" sections.
>         
>         For example, using "-O2" for $CFLAGS indicates that
>         "-fstrict-aliasing" is
>         used, but it is not used with "-O1."
>         
>         It also shows that with "-O2" the option "-mno-sse4" is used,
>         and so if
>         you want to use SSE4 for certain programs (e.g. video, audio)
>         you will
>         need to specifically enable it.
>         
>         There may be an even slicker way to reveal the flags, but this
>         is the
>         only way I know.
>         
>         Frank Peters
> 

An example of the issue discussed
https://bugs.gentoo.org/show_bug.cgi?id=347818

see in particular comment #3 they are understaffed and have a ton to do
but in the norm don't care to here it.

https://bugs.gentoo.org/show_bug.cgi?id=339485

Is a discussion/flame about the report upstream qa messages.
Help me out here guys and weigh in. (dons flame suit)

Further on the conversations wandered-to in the topic 'optimization'
in the kernel config menu under the heading 'General Setup' lies
        [*] Optimize trace point call sites 

CONFIG_JUMP_LABEL:                                                                                    
                                                                                                          
If it is detected that the compiler has support for "asm goto", the
kernel will compile trace point locations with just a nop instruction.
When trace points are enabled, the nop will be converted to a jump to
the trace function. This technique lowers overhead and stress on the
branch prediction of the processor.

I've had this checked for a good deal of time and see no issues because
of it.

David J Cozatt
aka user99
                                                                                 



Replies:
Re: Digest of gentoo-amd64@g.o issue 367 (13009-13035)
-- Duncan
Re: Re: Digest of gentoo-amd64@g.o issue 367 (13009-13035)
-- Frank Peters
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Updated Jun 28, 2012

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