[gentoo-user] cpu flags / USE flags / compiler flags

[Mark Knecht <markknecht@gmail.com>]

Hi,
   I've just recently (the last 4 or 5 days) been experiencing some
lock-ups on Firefox. As far as I can tell these seem to come only when
visiting certain web pages that have more multimedia content. When
Firefox locks up it can be killed from a terminal and restarted. There
are no messages in dmesg or /var/log/messages.

   In reviewing changes recently made I noted that the newest thing,
for me, was changing some USE flags. What I thought I was doing was
better matching the processor in each machine but possibly this is
causing the problem.

   On my laptop, a P4 / ATI machine, I went about it like this:

flash ~ #  cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 15
model           : 2
model name      : Mobile Intel(R) Pentium(R) 4     CPU 3.06GHz
stepping        : 9
cpu MHz         : 3067.965
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe cid
xtpr
bogomips        : 6078.46

flash ~ #

I then looked for CPU flags that had an equivalent USE flag and that
might be of use for faster graphics. On this machine I chose mmx, sse
& sse2. Armed with that I changed my make.conf file to look like this:

# These settings were set by the catalyst build script that
automatically built this stage
CFLAGS="-O2 -march=pentium4 -pipe -fomit-frame-pointer"
CHOST="i686-pc-linux-gnu"
USE="mmx sse sse2 gnome kde -arts ladspa nptl nptlonly ladcca
audiofile gimp gimpprint ppds usb alsa cdr dvd dvdr dvdread caps jack
jack-tmpfs fluidsynth tcltk sndfile v4l v4l2 mysql flac xscreensaver
samba i8x0 mythtv apache2 lirc mjpeg xvid real"
CXXFLAGS="${CFLAGS}"
MAKEOPTS="-j2"
GENTOO_MIRRORS="http://mirror.tucdemonic.org/gentoo/
ftp://ftp.gtlib.cc.gatech.edu/pub/gentoo http://mirror.gentoo.gr.jp
http://www.zentek-international.com/mirrors/gentoo/"
ALSA_CARDS="atiixp"
VIDEO_CARDS="radeon"
PORTDIR_OVERLAY=/usr/local/portage

I should note that I only remember adding sse2. mmx and sse where
there before and I had no problems.

QUESTION 1: Is this the right way to go about doing this sort of
thing? Or are the CPU flags supposed to become part of the CFLAGS line
also?

QUESTION 2: Are there any known problems with sse2 support? I think
I've added this on 3 machines and all 3 machines have experienced at
least one, if not more, lockups.

Certainly I can just remove the sse2 flag and recompile but I thought
I'd ask first.

Thanks,
Mark

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