240 lines
9.8 KiB
XML
240 lines
9.8 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" 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
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and Vulkan for 3D graphics; and OpenCL for general-purpose
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computing. This chapter describes how to set up GPU hardware
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acceleration (as far as this is not done automatically) and how to
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verify that hardware 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
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apply 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>
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is a general compute API. It is used by various applications such
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as 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
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Client Driver</emphasis> (ICD) mechanism. In this mechanism, an
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ICD file specifies the path to the OpenCL driver for a particular
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GPU family. In NixOS, there are two ways to make ICD files visible
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to the ICD loader. The first is through the
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<literal>OCL_ICD_VENDORS</literal> environment variable. This
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variable can contain a directory which is scanned by the ICL
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loader for ICD files. For example:
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</para>
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<programlisting>
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$ export \
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OCL_ICD_VENDORS=`nix-build '<nixpkgs>' --no-out-link -A rocm-opencl-icd`/etc/OpenCL/vendors/
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</programlisting>
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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
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the ICD file under <literal>/run/opengl-driver</literal>, where it
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will 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 <literal>clinfo</literal> command of the clinfo package. This
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command will report the number of hardware devices that is found
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and give detailed information for each device:
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</para>
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<programlisting>
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$ 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.
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</programlisting>
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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
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<link 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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rocm-opencl-icd package. Adding this package to
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<xref linkend="opt-hardware.opengl.extraPackages" /> enables
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OpenCL support:
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</para>
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<programlisting language="bash">
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hardware.opengl.extraPackages = [
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rocm-opencl-icd
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];
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</programlisting>
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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 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 intel-compute-runtime package.
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For Gen7 GPUs, the deprecated Beignet runtime can be used, which
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is provided by the beignet package. The proprietary Intel OpenCL
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runtime, in the intel-ocl package, is an alternative for Gen7
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GPUs.
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</para>
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<para>
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The intel-compute-runtime, beignet, or intel-ocl package can be
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added to <xref linkend="opt-hardware.opengl.extraPackages" /> to
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enable OpenCL support. For example, for Gen8 and later GPUs, the
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following configuration can be used:
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</para>
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<programlisting language="bash">
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hardware.opengl.extraPackages = [
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intel-compute-runtime
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];
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</programlisting>
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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>
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is a graphics and compute API for GPUs. It is used directly by
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games or indirectly though compatibility layers like
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<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" />
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is enabled, mesa is installed and provides Vulkan for supported
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hardware.
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</para>
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<para>
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Similar to OpenCL, Vulkan drivers are loaded through the
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<emphasis>Installable Client Driver</emphasis> (ICD) mechanism.
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ICD files for Vulkan are JSON files that specify the path to the
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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
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applications: an 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
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<literal>VK_ICD_FILENAMES</literal> environment variable. This
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variable can contain multiple JSON files, separated by
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<literal>:</literal>. For example:
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</para>
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<programlisting>
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$ export \
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VK_ICD_FILENAMES=`nix-build '<nixpkgs>' --no-out-link -A amdvlk`/share/vulkan/icd.d/amd_icd64.json
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</programlisting>
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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
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the ICD file under <literal>/run/opengl-driver</literal>, where it
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will 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 <literal>vulkaninfo</literal> command of the vulkan-tools
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package. This command will report the hardware devices and drivers
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found, in this example output amdvlk and radv:
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</para>
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<programlisting>
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$ 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
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</programlisting>
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<para>
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A simple graphical application that uses Vulkan is
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<literal>vkcube</literal> from the vulkan-tools 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
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<link 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,
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which is part of mesa, or the amdvlk package. Adding the amdvlk
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package to <xref linkend="opt-hardware.opengl.extraPackages" />
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makes amdvlk the default driver and hides radv and lavapipe from
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the device list. A specific driver can be forced as follows:
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</para>
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<programlisting language="bash">
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hardware.opengl.extraPackages = [
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pkgs.amdvlk
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];
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# To enable Vulkan support for 32-bit applications, also add:
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hardware.opengl.extraPackages32 = [
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pkgs.driversi686Linux.amdvlk
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];
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# Force radv
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environment.variables.AMD_VULKAN_ICD = "RADV";
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# Or
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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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</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
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default configuration, GPU devices have world-read/write
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permissions (<literal>/dev/dri/renderD*</literal>) or are tagged
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as <literal>uaccess</literal>
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(<literal>/dev/dri/card*</literal>). The access control lists of
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devices with the <literal>uaccess</literal> tag will be updated
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automatically when a user logs in through
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<literal>systemd-logind</literal>. 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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</para>
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<programlisting>
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$ 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::---
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</programlisting>
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<para>
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If you disabled (this functionality of)
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<literal>systemd-logind</literal>, you may need to add the user
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to the <literal>video</literal> group and 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
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address space using <literal>dlopen</literal>. Mixing an ICD
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loader mechanism and runtimes from different version of nixpkgs
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may not work. For example, if the ICD loader uses an older
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version of glibc than the runtime, the runtime may not be
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loadable due to missing symbols. Unfortunately, the loader will
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generally be quiet 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
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mismatches between an ICL loader and a runtime, you could run an
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application with the <literal>LD_DEBUG</literal> variable set to
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get more diagnostic information. For example, OpenCL can be
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tested with <literal>LD_DEBUG=files clinfo</literal>, which
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should report missing 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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