AMD64/FAQ

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The Gentoo AMD64 Frequently Asked Questions article.

See also
See also the main FAQ, or the Portage FAQ for frequently asked questions about the package manager. There is also a FAQ secion in the handbook. For frequently asked questions relating to the documentation wiki and editing the wiki, see the wiki FAQ. There are also other architecture-specific FAQs, such as: PPC/FAQ, MIPS/FAQ, and Alpha/FAQ.

Article status

This article has some todo items:

Add instructions for Cool'n'Quiet/PowerNow/SpeedStep for systemd users

Introduction

This document contains the most commonly asked questions about using Gentoo Linux on amd64 systems. Many of these questions come from the forums, IRC, and various mailing lists. The AMD64 Project provides support for Gentoo Linux on this architecture. For suggestions or questions about this FAQ, please leave a comment on the associated talk page.

Installation

What's the difference between AMD64 and EM64T?

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 be used?

Simple CFLAGS should be used, to avoid future problems. Supported CFLAGS values are -O2 -march=native -pipe for both AMD and Intel (EM64T) systems.

What kernel to use?

Almost all kernel sources available in Portage can be used. sys-kernel/gentoo-sources is recommended 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 the IA32_EMULATION option is activated in the kernel.

root #

cd /usr/src/linux

root #make menuconfig

KERNEL Enabling IA32 emulation

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

Warning
Build failures on multilib systems may occur if this option is deactivated.

Will using a 64-bit system instead of 32-bit improve performance?

That is a difficult question to answer. In some cases, there may be a performance improvement, in other cases 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 be of interest. There's also a nice thread, Article: 64-bit performance in Gentoo Linux in the forums.

Most systems will now be 64-bit unless there is a specific requirement otherwise.

What is multilib and how to use it?

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

Warning
Switching from a no-multilib to a multilib-enabled profile is currently not supported, a decision to use the no-multilib profile must be very carefully considered. If in doubt, choose multilib.

How to create a 32-bit chroot?

Please read the 32-bit Chroot Guide.

Is it possible to upgrade from an x86 system to AMD64 by doing emerge -e @world?

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. A database would need to be dumped 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.

Hardware

Will binary NVIDIA/ATI drivers work?

Yes, NVIDIA and ATI provide drivers that work on AMD64. Either x11-drivers/nvidia-drivers or x11-drivers/xf86-video-ati can be installed. See also the nvidia-drivers guide or the ATI FAQ.

How to use Cool'n'Quiet/PowerNow/SpeedStep features?

Custom kernel users must compile the kernel with support for these features. Enable the features below:

KERNEL Kernel options for Cool'n'Quiet/PowerNow/SpeedStep

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.

FILE /etc/conf.d/cpupowerExample configuration

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

root #rc-update add cpupower boot

Note
Read the Power Management Guide for more tips on CPU power management.

Applications

Upon installing package foo, emerge says: (masked by: ~amd64 keyword)

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

Upon installing package foo, emerge says: (masked by: missing keyword)

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

root #

echo "category/packagename **" >> /etc/portage/package.accept_keywords

root #emerge packagename

If the package works well, please file a bug on Gentoo's Bugzilla, so that the AMD64 team can keyword the package and other users can benefit.

Warning
Do not try to invoke commands like ACCEPT_KEYWORDS="~x86" emerge packagename. It will most certainly break the Portage tree and render the system useless.