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doc/overlays.xml: fix missing documentation for blas/lapack

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This adds some more information to the documentation as well as
addressing review from https://github.com/NixOS/nixpkgs/pull/85636.
This commit is contained in:
Matthew Bauer 2020-04-22 12:43:14 -05:00
parent 3d18975478
commit 4238b2b943
1 changed files with 21 additions and 10 deletions
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31
doc/using/overlays.xml
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@ -140,8 +140,8 @@ self: super:
<section xml:id="sec-overlays-alternatives">
<title>Using overlays to configure alternatives</title>
<para>
Certain software has different implementations of the same
interface. Other distributions have functionality to switch
Certain software packages have different implementations of the
same interface. Other distributions have functionality to switch
between these. For example, Debian provides <link
xlink:href="https://wiki.debian.org/DebianAlternatives">DebianAlternatives</link>.
Nixpkgs has what we call <literal>alternatives</literal>, which
@ -160,8 +160,9 @@ self: super:
</para>
<para>
The Nixpkgs attribute is <literal>openblas</literal> for
ILP64 and <literal>openblasCompat</literal> for LP64. This
is the default.
ILP64 (integer width = 64 bits) and
<literal>openblasCompat</literal> for LP64 (integer width =
32 bits). <literal>openblasCompat</literal> is the default.
</para>
</listitem>
<listitem>
@ -190,8 +191,15 @@ self: super:
#83888</link>, we are able to override the ‘blas’ and ‘lapack’
packages to use different implementations, through the
‘blasProvider’ and ‘lapackProvider’ argument. This can be used
to select a different provider. For example, an overlay can be
created that looks like:
to select a different provider. BLAS providers will have
symlinks in <literal>$out/lib/libblas.so.3</literal> and
<literal>$out/lib/libcblas.so.3</literal> to their respective
BLAS libraries. Likewise, LAPACK providers will have symlinks
in <literal>$out/lib/liblapack.so.3</literal> and
<literal>$out/lib/liblapacke.so.3</literal> to their respective
LAPCK libraries. For example, Intel MKL is both a BLAS and
LAPACK provider. An overlay can be created to use Intel MKL
that looks like:
</para>
<programlisting>
self: super:
@ -208,9 +216,12 @@ self: super:
<para>
This overlay uses Intel’s MKL library for both BLAS and LAPACK
interfaces. Note that the same can be accomplished at runtime
using <literal>LD_PRELOAD</literal> of libblas.so.3 and
liblapack.so.3.
using <literal>LD_LIBRARY_PATH</literal> of libblas.so.3 and
liblapack.so.3. For instance:
</para>
<programlisting>
$ LD_LIBRARY_PATH=$(nix-build -A mkl):$LD_LIBRARY_PATH nix-shell -p octave --run octave
</programlisting>
<para>
Intel MKL requires an <literal>openmp</literal> implementation
when running with multiple processors. By default,
@ -221,8 +232,8 @@ self: super:
set it with <literal>LD_PRELOAD</literal>. Note that
<literal>mkl</literal> is only available on
<literal>x86_64-linux</literal> and
<literal>x86_64-darwin</literal>. Moreover, Hydra is not build
and distributing pre-compiled binaries using it.
<literal>x86_64-darwin</literal>. Moreover, Hydra is not
building and distributing pre-compiled binaries using it.
</para>
<para>
For BLAS/LAPACK switching to work correctly, all packages must