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doc/overlays.xml: update documentation for BLAS/LAPACK

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This expands the documentation and explains how to assert LP64.
This commit is contained in:
Matthew Bauer 2020-04-21 11:03:10 -05:00
parent 8f58fa044d
commit 3c41d61514
2 changed files with 42 additions and 27 deletions
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29
doc/languages-frameworks/python.section.md
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@ -1290,32 +1290,9 @@ self: super: {
### How to use Intel's MKL with numpy and scipy?
A `site.cfg` is created that configures BLAS based on the `blas` parameter of
the `numpy` derivation. By passing in `mkl`, `numpy` and packages depending on
`numpy` will be built with `mkl`.
The following is an overlay that configures `numpy` to use `mkl`:
```nix
self: super: {
python37 = super.python37.override {
packageOverrides = python-self: python-super: {
numpy = python-super.numpy.override {
blas = super.pkgs.mkl;
};
};
};
}
```
`mkl` requires an `openmp` implementation when running with multiple processors.
By default, `mkl` will use Intel's `iomp` implementation if no other is
specified, but this is a runtime-only dependency and binary compatible with the
LLVM implementation. To use that one instead, Intel recommends users set it with
`LD_PRELOAD`.
Note that `mkl` is only available on `x86_64-{linux,darwin}` platforms;
moreover, Hydra is not building and distributing pre-compiled binaries using it.
MKL can be configured using an overlay. See the section “[Using
overlays to configure
alternatives](#sec-overlays-alternatives-blas-lapack)”.
### What inputs do `setup_requires`, `install_requires` and `tests_require` map to?

40
doc/using/overlays.xml
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@ -177,7 +177,7 @@ self: super:
<para>
<link
xlink:href="https://software.intel.com/en-us/mkl">Intel
MKL</link> (only works on x86 architecture)
MKL</link> (only works on x86 architecture, unfree)
</para>
<para>
The Nixpkgs attribute is <literal>mkl</literal>.
@ -211,6 +211,44 @@ self: super:
using <literal>LD_PRELOAD</literal> of libblas.so.3 and
liblapack.so.3.
</para>
<para>
Intel MKL requires an <literal>openmp</literal> implementation
when running with multiple processors. By default,
<literal>mkl</literal> will use Intel’s <literal>iomp</literal>
implementation if no other is specified, but this is a
runtime-only dependency and binary compatible with the LLVM
implementation. To use that one instead, Intel recommends users
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.
</para>
<para>
For BLAS/LAPACK switching to work correctly, all packages must
depend on <literal>blas</literal> or <literal>lapack</literal>.
This ensures that only one BLAS/LAPACK library is used at one
time. There are two versions versions of BLAS/LAPACK currently
in the wild, <literal>LP64</literal> (integer size = 32 bits)
and <literal>ILP64</literal> (integer size = 64 bits). Some
software needs special flags or patches to work with
<literal>ILP64</literal>. You can check if
<literal>ILP64</literal> is used in Nixpkgs with
<varname>blas.isILP64</varname> and
<varname>lapack.isILP64</varname>. Some software does NOT work
with <literal>ILP64</literal>, and derivations need to specify
an assertion to prevent this. You can prevent
<literal>ILP64</literal> from being used with the following:
</para>
<programlisting>
{ stdenv, blas, lapack, ... }:
assert (!blas.isILP64) &amp;&amp; (!lapack.isILP64);
stdenv.mkDerivation {
...
}
</programlisting>
</section>
</section>
</chapter>