Jonathan Peyton 2ff3850ea1
[OpenMP] Add absolute KMP_HW_SUBSET functionality (#85326)
Users can put a : in front of KMP_HW_SUBSET to indicate that the
specified subset is an "absolute" subset. Currently, when a user puts
KMP_HW_SUBSET=1t. This gets translated to KMP_HW_SUBSET="*s,*c,1t",
where * means "use all of". If a user wants only one thread as the
entire topology they can now do KMP_HW_SUBSET=:1t.

Along with the absolute syntax is a fix for newer machines and making
them easier to use with only the 3-level topology syntax. When a user
puts KMP_HW_SUBSET=1s,4c,2t on a machine which actually has 4 layers,
(say 1s,2m,3c,2t as the entire machine) the user gets an unexpected "too
many resources asked" message because KMP_HW_SUBSET currently translates
the "4c" value to mean 4 cores per module. To help users out, the
runtime can assume that these newer layers, module in this case, should
be ignored if they are not specified, but the topology should always
take into account the sockets, cores, and threads layers.
2024-04-03 11:43:23 -05:00
..

OpenMP LLVM Documentation
==================

OpenMP LLVM's documentation is written in reStructuredText, a lightweight
plaintext markup language (file extension `.rst`). While the
reStructuredText documentation should be quite readable in source form, it
is mostly meant to be processed by the Sphinx documentation generation
system to create HTML pages which are hosted on <https://llvm.org/docs/> and
updated after every commit. Manpage output is also supported, see below.

If you instead would like to generate and view the HTML locally, install
Sphinx <http://sphinx-doc.org/> and then do:

    cd <build-dir>
    cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_HTML=true -DCMAKE_MODULE_PATH=/path/to/llvm/cmake/modules <src-dir>
    make docs-openmp-html
    $BROWSER <build-dir>/docs/html/index.html

The mapping between reStructuredText files and generated documentation is
`docs/Foo.rst` <-> `<build-dir>/projects/openmp/docs//html/Foo.html` <->
`https://openmp.llvm.org/docs/Foo.html`.

If you are interested in writing new documentation, you will want to read
`llvm/docs/SphinxQuickstartTemplate.rst` which will get you writing
documentation very fast and includes examples of the most important
reStructuredText markup syntax.

Manpage Output
===============

Building the manpages is similar to building the HTML documentation. The
primary difference is to use the `man` makefile target, instead of the
default (which is `html`). Sphinx then produces the man pages in the
directory `<build-dir>/docs/man/`.

    cd <build-dir>
    cmake -DLLVM_ENABLE_SPHINX=true -DSPHINX_OUTPUT_MAN=true <src-dir>
    make
    man -l >build-dir>/docs/man/FileCheck.1

The correspondence between .rst files and man pages is
`docs/CommandGuide/Foo.rst` <-> `<build-dir>/projects/openmp/docs//man/Foo.1`.
These .rst files are also included during HTML generation so they are also
viewable online (as noted above) at e.g.
`https://openmp.llvm.org/docs/CommandGuide/Foo.html`.