258 lines
9.9 KiB
XML
258 lines
9.9 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xmlns:xi="http://www.w3.org/2001/XInclude"
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version="5.0"
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xml:id="sec-gpu-accel">
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<title>GPU acceleration</title>
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<para>
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NixOS provides various APIs that benefit from GPU hardware
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acceleration, such as VA-API and VDPAU for video playback; OpenGL and
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Vulkan for 3D graphics; and OpenCL for general-purpose computing.
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This chapter describes how to set up GPU hardware acceleration (as far
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as this is not done automatically) and how to verify that hardware
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acceleration is indeed used.
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</para>
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<para>
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Most of the aforementioned APIs are agnostic with regards to which
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display server is used. Consequently, these instructions should apply
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both to the X Window System and Wayland compositors.
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</para>
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<section xml:id="sec-gpu-accel-opencl">
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<title>OpenCL</title>
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<para>
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<link xlink:href="https://en.wikipedia.org/wiki/OpenCL">OpenCL</link> is a
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general compute API. It is used by various applications such as
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Blender and Darktable to accelerate certain operations.
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</para>
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<para>
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OpenCL applications load drivers through the <emphasis>Installable Client
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Driver</emphasis> (ICD) mechanism. In this mechanism, an ICD file
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specifies the path to the OpenCL driver for a particular GPU family.
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In NixOS, there are two ways to make ICD files visible to the ICD
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loader. The first is through the <varname>OCL_ICD_VENDORS</varname>
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environment variable. This variable can contain a directory which
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is scanned by the ICL loader for ICD files. For example:
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<screen><prompt>$</prompt> export \
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OCL_ICD_VENDORS=`nix-build '<nixpkgs>' --no-out-link -A rocm-opencl-icd`/etc/OpenCL/vendors/</screen>
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</para>
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<para>
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The second mechanism is to add the OpenCL driver package to
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<xref linkend="opt-hardware.opengl.extraPackages"/>. This links the
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ICD file under <filename>/run/opengl-driver</filename>, where it will
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be visible to the ICD loader.
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</para>
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<para>
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The proper installation of OpenCL drivers can be verified through
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the <command>clinfo</command> command of the <package>clinfo</package>
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package. This command will report the number of hardware devices
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that is found and give detailed information for each device:
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</para>
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<screen><prompt>$</prompt> clinfo | head -n3
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Number of platforms 1
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Platform Name AMD Accelerated Parallel Processing
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Platform Vendor Advanced Micro Devices, Inc.</screen>
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<section xml:id="sec-gpu-accel-opencl-amd">
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<title>AMD</title>
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<para>
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Modern AMD <link
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xlink:href="https://en.wikipedia.org/wiki/Graphics_Core_Next">Graphics
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Core Next</link> (GCN) GPUs are supported through the
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<package>rocm-opencl-icd</package> package. Adding this package to
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<xref linkend="opt-hardware.opengl.extraPackages"/> enables OpenCL
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support:
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<programlisting><xref linkend="opt-hardware.opengl.extraPackages"/> = [
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rocm-opencl-icd
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];</programlisting>
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</para>
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</section>
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<section xml:id="sec-gpu-accel-opencl-intel">
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<title>Intel</title>
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<para>
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<link
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xlink:href="https://en.wikipedia.org/wiki/List_of_Intel_graphics_processing_units#Gen8">Intel
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Gen8 and later GPUs</link> are supported by the Intel NEO OpenCL
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runtime that is provided by the
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<package>intel-compute-runtime</package> package. For Gen7 GPUs,
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the deprecated Beignet runtime can be used, which is provided
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by the <package>beignet</package> package. The proprietary Intel
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OpenCL runtime, in the <package>intel-ocl</package> package, is
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an alternative for Gen7 GPUs.
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</para>
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<para>
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The <package>intel-compute-runtime</package>, <package>beignet</package>,
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or <package>intel-ocl</package> package can be added to
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<xref linkend="opt-hardware.opengl.extraPackages"/> to enable OpenCL
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support. For example, for Gen8 and later GPUs, the following
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configuration can be used:
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<programlisting><xref linkend="opt-hardware.opengl.extraPackages"/> = [
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intel-compute-runtime
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];</programlisting>
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</para>
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</section>
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</section>
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<section xml:id="sec-gpu-accel-vulkan">
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<title>Vulkan</title>
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<para>
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<link xlink:href="https://en.wikipedia.org/wiki/Vulkan_(API)">Vulkan</link> is a
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graphics and compute API for GPUs. It is used directly by games or indirectly though
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compatibility layers like <link xlink:href="https://github.com/doitsujin/dxvk/wiki">DXVK</link>.
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</para>
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<para>
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By default, if <xref linkend="opt-hardware.opengl.driSupport"/> is enabled,
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<package>mesa</package> is installed and provides Vulkan for supported hardware.
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</para>
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<para>
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Similar to OpenCL, Vulkan drivers are loaded through the <emphasis>Installable Client
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Driver</emphasis> (ICD) mechanism. ICD files for Vulkan are JSON files that specify
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the path to the driver library and the supported Vulkan version. All successfully
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loaded drivers are exposed to the application as different GPUs.
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In NixOS, there are two ways to make ICD files visible to Vulkan applications: an
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environment variable and a module option.
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</para>
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<para>
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The first option is through the <varname>VK_ICD_FILENAMES</varname>
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environment variable. This variable can contain multiple JSON files, separated by
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<literal>:</literal>. For example:
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<screen><prompt>$</prompt> export \
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VK_ICD_FILENAMES=`nix-build '<nixpkgs>' --no-out-link -A amdvlk`/share/vulkan/icd.d/amd_icd64.json</screen>
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</para>
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<para>
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The second mechanism is to add the Vulkan driver package to
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<xref linkend="opt-hardware.opengl.extraPackages"/>. This links the
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ICD file under <filename>/run/opengl-driver</filename>, where it will
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be visible to the ICD loader.
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</para>
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<para>
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The proper installation of Vulkan drivers can be verified through
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the <command>vulkaninfo</command> command of the <package>vulkan-tools</package>
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package. This command will report the hardware devices and drivers found,
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in this example output amdvlk and radv:
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</para>
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<screen><prompt>$</prompt> vulkaninfo | grep GPU
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GPU id : 0 (Unknown AMD GPU)
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GPU id : 1 (AMD RADV NAVI10 (LLVM 9.0.1))
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...
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GPU0:
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deviceType = PHYSICAL_DEVICE_TYPE_DISCRETE_GPU
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deviceName = Unknown AMD GPU
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GPU1:
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deviceType = PHYSICAL_DEVICE_TYPE_DISCRETE_GPU</screen>
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<para>
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A simple graphical application that uses Vulkan is <command>vkcube</command>
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from the <package>vulkan-tools</package> package.
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</para>
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<section xml:id="sec-gpu-accel-vulkan-amd">
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<title>AMD</title>
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<para>
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Modern AMD <link
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xlink:href="https://en.wikipedia.org/wiki/Graphics_Core_Next">Graphics
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Core Next</link> (GCN) GPUs are supported through either radv, which is
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part of <package>mesa</package>, or the <package>amdvlk</package> package.
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Adding the <package>amdvlk</package> package to
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<xref linkend="opt-hardware.opengl.extraPackages"/> makes both drivers
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available for applications and lets them choose. A specific driver can
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be forced as follows:
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<programlisting><xref linkend="opt-hardware.opengl.extraPackages"/> = [
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<package>amdvlk</package>
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];
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# For amdvlk
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<xref linkend="opt-environment.variables"/>.VK_ICD_FILENAMES =
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"/run/opengl-driver/share/vulkan/icd.d/amd_icd64.json";
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# For radv
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<xref linkend="opt-environment.variables"/>.VK_ICD_FILENAMES =
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"/run/opengl-driver/share/vulkan/icd.d/radeon_icd.x86_64.json";
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</programlisting>
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</para>
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</section>
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</section>
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<section xml:id="sec-gpu-accel-common-issues">
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<title>Common issues</title>
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<section xml:id="sec-gpu-accel-common-issues-permissions">
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<title>User permissions</title>
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<para>
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Except where noted explicitly, it should not be necessary to
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adjust user permissions to use these acceleration APIs. In the default
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configuration, GPU devices have world-read/write permissions
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(<filename>/dev/dri/renderD*</filename>) or are tagged as
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<code>uaccess</code> (<filename>/dev/dri/card*</filename>). The
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access control lists of devices with the <varname>uaccess</varname>
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tag will be updated automatically when a user logs in through
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<command>systemd-logind</command>. For example, if the user
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<emphasis>jane</emphasis> is logged in, the access control list
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should look as follows:
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<screen><prompt>$</prompt> getfacl /dev/dri/card0
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# file: dev/dri/card0
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# owner: root
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# group: video
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user::rw-
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user:jane:rw-
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group::rw-
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mask::rw-
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other::---</screen>
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If you disabled (this functionality of) <command>systemd-logind</command>,
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you may need to add the user to the <code>video</code> group and
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log in again.
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</para>
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</section>
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<section xml:id="sec-gpu-accel-common-issues-mixing-nixpkgs">
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<title>Mixing different versions of nixpkgs</title>
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<para>
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The <emphasis>Installable Client Driver</emphasis> (ICD)
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mechanism used by OpenCL and Vulkan loads runtimes into its address
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space using <code>dlopen</code>. Mixing an ICD loader mechanism and
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runtimes from different version of nixpkgs may not work. For example,
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if the ICD loader uses an older version of <package>glibc</package>
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than the runtime, the runtime may not be loadable due to
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missing symbols. Unfortunately, the loader will generally be quiet
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about such issues.
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</para>
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<para>
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If you suspect that you are running into library version mismatches
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between an ICL loader and a runtime, you could run an application with
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the <code>LD_DEBUG</code> variable set to get more diagnostic
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information. For example, OpenCL can be tested with
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<code>LD_DEBUG=files clinfo</code>, which should report missing
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symbols.
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</para>
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</section>
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</section>
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</chapter>
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