Re: Performance problems between gcc 12.2 and 13

[Andreas Jaeger <aj at suse dot com>]

On Tuesday, July 17, 2012 16:47:37 Carlos O'Donell wrote:
> On 7/17/2012 4:22 PM, Judd Montgomery wrote:
> > After upgrading a server I have noticed that a few applications run
> > quite a bit slower.
> Could we please move this to libc-help until we have something
> specific to talk about in terms of a patch or reported bug?
> 
> Please remove libc-alpha from future responses.
> 
> > At least one cause and maybe the only cause looks to be in the
> > eglibc libraries.  I compiled eglibc, found some performance
> > differences and then compiled glibc versions to see if they had the
> > same performance differences and they do.  The slowness appeared
> > between versions 2.12.2 and 2.13 and continues in 2.16.
> > 
> > Here is one example, I can come up with other functions with
> > performance degredations as well.  Does anyone know why and how to
> > fix it?
> You've become your own distribution, and as such you must pay careful
> attention to the compiler and binary utilities you used to compile
> glibc.
> > I compiled glibc with the following:
> > $ env CFLAGS='-O2 -U_FORTIFY_SOURCE -fno-stack-protector'
> > ../../src/$VERSION/configure --enable-omitfp --prefix=/opt/$VERSION
> > --enable-add-ons && make && sudo make install
> You should be running `make check' to ensure your build and
> environment are working.
> > I compiled a test program with:
> > $ export VERSION=glibc-2.13; gcc -Wall -Xlinker
> > -rpath=/opt/$VERSION/lib -Xlinker
> > -I/opt/$VERSION/lib/ld-linux-x86-64.so.2 loop.c -o loop.13 $ export
> > VERSION=glibc-2.12.2; gcc -Wall -Xlinker -rpath=/opt/$VERSION/lib
> > -Xlinker -I/opt/$VERSION/lib/ld-linux-x86-64.so.2 loop.c -o loop.12
> How does this compare to 2.16?
> 
> The x86_64 support has multiple string functions optimized for
> different processor variants.

And for that you need to add --enable-multi-arch,

Andreas
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