Gentoo Archives: gentoo-amd64

From: DJ Cozatt <ygdrasil@×××××××.net>
To: gentoo-amd64@l.g.o
Subject: [gentoo-amd64] Re: Digest of gentoo-amd64@lists.gentoo.org issue 367 (13009-13035)
Date: Fri, 08 Jul 2011 21:03:54
Message-Id: 1310157998.2676.16.camel@random.mshome
On Tue, 2011-07-05 at 13:02 +0000, gentoo-amd64+help@l.g.o
wrote:
> On Thu, 30 Jun 2011 21:36:38 -0700 > Mark Knecht <markknecht@×××××.com> 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

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