AMD64/FAQ

What's the difference between AMD64 and EM64T?[edit | edit source]

Both refer to 64-bit processors, one from AMD (AMD64) and the other from Intel (EM64T). AMD's 64-bit processors include the Athlon 64, Opteron, Turion, Neo, Phenom, FX, AX/EX/CX, Ryzen and EPYC families. Intel's 64-bit processors include the Core 2, Core iX, Celeron, Xeon, and Pentium (all based on the Core 2 architecture and later). The last few versions of the old Pentium 4 and Xeon chips also support EM64T.

The AMD line of 64-bit processors were released well ahead of Intel's offering. Therefore, for historical reasons, the arch keyword for all x86-64 compatible architectures in Gentoo is amd64. As such, AMD64 is a generic reference to 64-bit chips, whether AMD or Intel.

What CFLAGS should I use?[edit | edit source]

You should use simple CFLAGS to avoid future problems with your system. Supported CFLAGS values are -O2 -march=native -pipe for both AMD and Intel (EM64T) systems.

What kernel should I use?[edit | edit source]

You can use almost all kernel sources available in Portage. We recommend using sys-kernel/gentoo-sources because it is a special kernel designed for Gentoo Linux. It contains lots of AMD64-specific patches and therefore is the only kernel officially supported by Gentoo/AMD64.

Make sure you have the IA32_EMULATION option activated in the kernel.

Executable file formats / Emulations  --->
  [*] IA32 Emulation

Will I have a performance upgrade if I use a 64-bit system instead of 32-bit?[edit | edit source]

That is a difficult question to answer. In some cases, you will experience a performance improvement, in other cases you will not. For everyday use, there is almost no difference between 64-bit and 32-bit. 64-bit is generally faster when it comes to floating point computing, which is normally the case in multimedia applications and 3D rendering. Linux.com's articles 64-bit performance in Gentoo Linux and 64-bit Linux and BSD are maturing steadily may interest you. There's also a nice thread, Article: 64-bit performance in Gentoo Linux in our forums.

What is multilib and how can I use it?[edit | edit source]

Every AMD64 processor is able to run 32-bit code as well as 64-bit code. However, when you have a 32-bit application, you are unable to mix it with 64-bit libraries or vice versa. You can, however, natively (without emulation) run 32-bit applications if all shared libraries they need are available as 32-bit objects. You can choose whether you want multilib support or not by selecting the according profile. The default is a multilib-enabled profile.

How do I create a 32-bit chroot?[edit | edit source]

Please read the 32-bit Chroot Guide.

Can I upgrade from my x86 system to AMD64 by doing emerge -e @world?[edit | edit source]

Due to several differences between x86 (32-bit) and amd64 (64-bit) installations, it is impossible to upgrade this way. Please perform a fresh install using the AMD64 Handbook.

Note that binary files created on an x86 system most likely cannot be read by packages on an AMD64 system. In particular, some databases, such as OpenLDAP, cannot simply be copied as-is. You will need to dump the database into an architecture-independent format, such as a text file, before attempting to restore it on an AMD64 system. Database files for MySQL, Berkley DB and SQLite are architecture-independent and can be moved freely after their corresponding daemons, if any, are cleanly shut down.

Will my binary NVIDIA/ATI drivers work?[edit | edit source]

Yes, NVIDIA and ATI provide drivers that work on AMD64. You can install either x11-drivers/nvidia-drivers or x11-drivers/xf86-video-ati. If you have more questions about these drivers, you should read the nvidia-drivers guide or the ATI FAQ.

How do I use Cool'n'Quiet/PowerNow/SpeedStep features?[edit | edit source]

You have to compile your kernel with support for these features. You just need to enable the features below:

Power management and ACPI options --->
  [*] Device power management core functionality
  [*] ACPI (Advanced Configuration and Power Interface) Support --->
    <*>   Processor
    <*>     Thermal Zone
  CPU Frequency scaling --->
  [*] CPU Frequency scaling
         Default CPUFreq governor (ondemand) --->
  -*-   'performance' governor
  <*>   'userspace' governor for userspace frequency scaling
  -*-   'ondemand' cpufreq policy governor
  <*>   ACPI Processor P-States driver
  CPU Idle  --->
    -*- CPU idle PM support

Then install sys-power/cpupower and edit /etc/conf.d/cpupower with a preferred text editor.

# Options when starting cpufreq (given to the `cpupower` program)
START_OPTS="--governor ondemand"
  
# Options when stopping cpufreq (given to the `cpupower` program)
STOP_OPTS="--governor performance"

Now you have to run the following command to make sure the cpupower daemon is started every time the system boots:

Can I get Adobe Flash working?[edit | edit source]

Yes. Install www-plugins/adobe-flash. Be sure to read any messages displayed by the ebuild once it has been emerged.

I want to install package foo, but emerge says: (masked by: ~amd64 keyword)[edit | edit source]

This means that the package is still in the 'testing' tree. Please read Portage's manual page (man portage) or the Mixing Software Branches chapter of the AMD64 Handbook for more information.

I want to install package foo, but emerge says: (masked by: missing keyword)[edit | edit source]

This means that the package has not been tested yet. It does not necessarily mean that the package does not work. You can unmask it by accepting another architecture (or set of architectures) for the package. The following example shows you can tell Portage to accept the installation of the given package under any keyword.

If it works fine for you, please let us know and file a bug on Gentoo's Bugzilla, so that the AMD64 team can keyword the package and other users can benefit from your test.