Merge pull request #95336 from danieldk/gpu-accel-common-issues

nixos/manual: add a section about common GPU acceleration issues
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Daniël de Kok 2020-08-14 08:30:24 +02:00 committed by GitHub
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@ -190,4 +190,63 @@ GPU1:
</para>
</section>
</section>
<section xml:id="sec-gpu-accel-common-issues">
<title>Common issues</title>
<section xml:id="sec-gpu-accel-common-issues-permissions">
<title>User permissions</title>
<para>
Except where noted explicitly, it should not be necessary to
adjust user permissions to use these acceleration APIs. In the default
configuration, GPU devices have world-read/write permissions
(<filename>/dev/dri/renderD*</filename>) or are tagged as
<code>uaccess</code> (<filename>/dev/dri/card*</filename>). The
access control lists of devices with the <varname>uaccess</varname>
tag will be updated automatically when a user logs in through
<command>systemd-logind</command>. For example, if the user
<emphasis>jane</emphasis> is logged in, the access control list
should look as follows:
<screen><prompt>$</prompt> getfacl /dev/dri/card0
# file: dev/dri/card0
# owner: root
# group: video
user::rw-
user:jane:rw-
group::rw-
mask::rw-
other::---</screen>
If you disabled (this functionality of) <command>systemd-logind</command>,
you may need to add the user to the <code>video</code> group and
log in again.
</para>
</section>
<section xml:id="sec-gpu-accel-common-issues-mixing-nixpkgs">
<title>Mixing different versions of nixpkgs</title>
<para>
The <emphasis>Installable Client Driver</emphasis> (ICD)
mechanism used by OpenCL and Vulkan loads runtimes into its address
space using <code>dlopen</code>. Mixing an ICD loader mechanism and
runtimes from different version of nixpkgs may not work. For example,
if the ICD loader uses an older version of <package>glibc</package>
than the runtime, the runtime may not be loadable due to
missing symbols. Unfortunately, the loader will generally be quiet
about such issues.
</para>
<para>
If you suspect that you are running into library version mismatches
between an ICL loader and a runtime, you could run an application with
the <code>LD_DEBUG</code> variable set to get more diagnostic
information. For example, OpenCL can be tested with
<code>LD_DEBUG=files clinfo</code>, which should report missing
symbols.
</para>
</section>
</section>
</chapter>